diff --git a/go/vehicle-gateway/cmd/stat-writer/main.go b/go/vehicle-gateway/cmd/stat-writer/main.go
new file mode 100644
index 00000000..fb6716d4
--- /dev/null
+++ b/go/vehicle-gateway/cmd/stat-writer/main.go
@@ -0,0 +1,122 @@
+package main
+
+import (
+	"context"
+	"database/sql"
+	"encoding/json"
+	"os"
+	"os/signal"
+	"strings"
+	"syscall"
+	"time"
+
+	_ "github.com/go-sql-driver/mysql"
+	"github.com/segmentio/kafka-go"
+
+	"lingniu-vehicle-ingest/go/vehicle-gateway/internal/envelope"
+	"lingniu-vehicle-ingest/go/vehicle-gateway/internal/observability"
+	"lingniu-vehicle-ingest/go/vehicle-gateway/internal/stats"
+)
+
+func main() {
+	logger := observability.NewLogger("vehicle-stat-writer")
+	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
+	defer stop()
+
+	cfg := loadConfig()
+	db, err := sql.Open("mysql", cfg.MySQLDSN)
+	if err != nil {
+		logger.Error("mysql open failed", "error", err)
+		os.Exit(1)
+	}
+	defer db.Close()
+	if err := db.PingContext(ctx); err != nil {
+		logger.Error("mysql ping failed", "error", err)
+		os.Exit(1)
+	}
+
+	writer := stats.NewWriter(db, cfg.Location)
+	if cfg.EnsureSchema {
+		if err := writer.EnsureSchema(ctx); err != nil {
+			logger.Error("mysql schema bootstrap failed", "error", err)
+			os.Exit(1)
+		}
+	}
+
+	reader := kafka.NewReader(kafka.ReaderConfig{
+		Brokers:     cfg.KafkaBrokers,
+		GroupID:     cfg.KafkaGroup,
+		GroupTopics: cfg.KafkaTopics,
+		MinBytes:    1,
+		MaxBytes:    10e6,
+	})
+	defer reader.Close()
+
+	logger.Info("stat writer started", "group", cfg.KafkaGroup, "topics", strings.Join(cfg.KafkaTopics, ","))
+	for {
+		message, err := reader.FetchMessage(ctx)
+		if err != nil {
+			if ctx.Err() != nil {
+				return
+			}
+			logger.Error("kafka fetch failed", "error", err)
+			continue
+		}
+		var env envelope.FrameEnvelope
+		if err := json.Unmarshal(message.Value, &env); err != nil {
+			logger.Warn("skip invalid envelope json", "topic", message.Topic, "partition", message.Partition, "offset", message.Offset, "error", err)
+			_ = reader.CommitMessages(ctx, message)
+			continue
+		}
+		if err := writer.Append(ctx, env); err != nil {
+			logger.Error("mysql append failed", "topic", message.Topic, "partition", message.Partition, "offset", message.Offset, "event_id", env.StableEventID(), "error", err)
+			continue
+		}
+		if err := reader.CommitMessages(ctx, message); err != nil {
+			logger.Error("kafka commit failed", "topic", message.Topic, "partition", message.Partition, "offset", message.Offset, "error", err)
+		}
+	}
+}
+
+type config struct {
+	KafkaBrokers []string
+	KafkaTopics  []string
+	KafkaGroup   string
+	MySQLDSN     string
+	EnsureSchema bool
+	Location     *time.Location
+}
+
+func loadConfig() config {
+	loc, err := time.LoadLocation(env("LOCAL_TZ", "Asia/Shanghai"))
+	if err != nil {
+		loc = time.FixedZone("Asia/Shanghai", 8*3600)
+	}
+	return config{
+		KafkaBrokers: splitCSV(env("KAFKA_BROKERS", "127.0.0.1:9092")),
+		KafkaTopics:  splitCSV(env("KAFKA_TOPICS", "vehicle.raw.gb32960.v1,vehicle.raw.jt808.v1")),
+		KafkaGroup:   env("KAFKA_GROUP", "go-stat-writer"),
+		MySQLDSN:     env("MYSQL_DSN", ""),
+		EnsureSchema: env("MYSQL_ENSURE_SCHEMA", "true") != "false",
+		Location:     loc,
+	}
+}
+
+func env(key string, fallback string) string {
+	value := strings.TrimSpace(os.Getenv(key))
+	if value == "" {
+		return fallback
+	}
+	return value
+}
+
+func splitCSV(value string) []string {
+	var out []string
+	for _, item := range strings.Split(value, ",") {
+		item = strings.TrimSpace(item)
+		if item != "" {
+			out = append(out, item)
+		}
+	}
+	return out
+}
diff --git a/go/vehicle-gateway/go.mod b/go/vehicle-gateway/go.mod
index f5c6af4f..f0ce1a80 100644
--- a/go/vehicle-gateway/go.mod
+++ b/go/vehicle-gateway/go.mod
@@ -3,11 +3,13 @@ module lingniu-vehicle-ingest/go/vehicle-gateway
 go 1.26
 
 require (
+	github.com/go-sql-driver/mysql v1.9.3
 	github.com/segmentio/kafka-go v0.4.49
 	github.com/taosdata/driver-go/v3 v3.8.1
 )
 
 require (
+	filippo.io/edwards25519 v1.1.0 // indirect
 	github.com/google/uuid v1.6.0 // indirect
 	github.com/gorilla/websocket v1.5.0 // indirect
 	github.com/json-iterator/go v1.1.12 // indirect
diff --git a/go/vehicle-gateway/go.sum b/go/vehicle-gateway/go.sum
index d5ca35d3..a65a9396 100644
--- a/go/vehicle-gateway/go.sum
+++ b/go/vehicle-gateway/go.sum
@@ -1,6 +1,10 @@
+filippo.io/edwards25519 v1.1.0 h1:FNf4tywRC1HmFuKW5xopWpigGjJKiJSV0Cqo0cJWDaA=
+filippo.io/edwards25519 v1.1.0/go.mod h1:BxyFTGdWcka3PhytdK4V28tE5sGfRvvvRV7EaN4VDT4=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/go-sql-driver/mysql v1.9.3 h1:U/N249h2WzJ3Ukj8SowVFjdtZKfu9vlLZxjPXV1aweo=
+github.com/go-sql-driver/mysql v1.9.3/go.mod h1:qn46aNg1333BRMNU69Lq93t8du/dwxI64Gl8i5p1WMU=
 github.com/google/gofuzz v1.0.0/go.mod h1:dBl0BpW6vV/+mYPU4Po3pmUjxk6FQPldtuIdl/M65Eg=
 github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
 github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
diff --git a/go/vehicle-gateway/internal/stats/daily_metric.go b/go/vehicle-gateway/internal/stats/daily_metric.go
new file mode 100644
index 00000000..468f5daa
--- /dev/null
+++ b/go/vehicle-gateway/internal/stats/daily_metric.go
@@ -0,0 +1,159 @@
+package stats
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"strconv"
+	"strings"
+	"time"
+
+	"lingniu-vehicle-ingest/go/vehicle-gateway/internal/envelope"
+)
+
+const (
+	MetricDailyMileageKM      = "daily_mileage_km"
+	MetricDailyTotalMileageKM = "daily_total_mileage_km"
+)
+
+type Execer interface {
+	ExecContext(context.Context, string, ...any) (sql.Result, error)
+}
+
+type Writer struct {
+	exec Execer
+	loc  *time.Location
+}
+
+type MetricSample struct {
+	VIN            string
+	Protocol       envelope.Protocol
+	StatDate       string
+	MetricKey      string
+	MetricValue    float64
+	TotalMileageKM float64
+}
+
+func NewWriter(exec Execer, loc *time.Location) *Writer {
+	if exec == nil {
+		panic("stats execer must not be nil")
+	}
+	if loc == nil {
+		loc = time.FixedZone("Asia/Shanghai", 8*3600)
+	}
+	return &Writer{exec: exec, loc: loc}
+}
+
+func (w *Writer) EnsureSchema(ctx context.Context) error {
+	_, err := w.exec.ExecContext(ctx, DailyMetricTableSQL)
+	return err
+}
+
+func (w *Writer) Append(ctx context.Context, env envelope.FrameEnvelope) error {
+	samples, err := SamplesFromEnvelope(env, w.loc)
+	if err != nil {
+		return err
+	}
+	for _, sample := range samples {
+		if _, err := w.exec.ExecContext(ctx, upsertDailyMetricSQL,
+			sample.VIN,
+			sample.StatDate,
+			string(sample.Protocol),
+			sample.MetricKey,
+			sample.MetricValue,
+			sample.TotalMileageKM,
+			sample.TotalMileageKM); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func SamplesFromEnvelope(env envelope.FrameEnvelope, loc *time.Location) ([]MetricSample, error) {
+	vin := strings.TrimSpace(env.VIN)
+	if vin == "" {
+		return nil, nil
+	}
+	totalMileage, ok := floatField(env, envelope.FieldTotalMileageKM)
+	if !ok {
+		return nil, nil
+	}
+	if loc == nil {
+		loc = time.FixedZone("Asia/Shanghai", 8*3600)
+	}
+	eventMS := env.EventTimeMS
+	if eventMS <= 0 {
+		eventMS = env.ReceivedAtMS
+	}
+	if eventMS <= 0 {
+		return nil, errors.New("event or received time is required")
+	}
+	statDate := time.UnixMilli(eventMS).In(loc).Format("2006-01-02")
+	return []MetricSample{
+		{
+			VIN:            vin,
+			Protocol:       env.Protocol,
+			StatDate:       statDate,
+			MetricKey:      MetricDailyMileageKM,
+			MetricValue:    0,
+			TotalMileageKM: totalMileage,
+		},
+		{
+			VIN:            vin,
+			Protocol:       env.Protocol,
+			StatDate:       statDate,
+			MetricKey:      MetricDailyTotalMileageKM,
+			MetricValue:    totalMileage,
+			TotalMileageKM: totalMileage,
+		},
+	}, nil
+}
+
+const upsertDailyMetricSQL = `
+INSERT INTO vehicle_daily_metric
+  (vin, stat_date, protocol, metric_key, metric_value, metric_unit,
+   first_total_mileage_km, latest_total_mileage_km, sample_count, calculation_method)
+VALUES (?, ?, ?, ?, ?, 'km', ?, ?, 1, 'TOTAL_MILEAGE_DIFF')
+ON DUPLICATE KEY UPDATE
+  first_total_mileage_km = LEAST(first_total_mileage_km, VALUES(first_total_mileage_km)),
+  latest_total_mileage_km = GREATEST(latest_total_mileage_km, VALUES(latest_total_mileage_km)),
+  metric_value = CASE
+    WHEN metric_key = 'daily_mileage_km'
+      THEN GREATEST(latest_total_mileage_km, VALUES(latest_total_mileage_km))
+           - LEAST(first_total_mileage_km, VALUES(first_total_mileage_km))
+    WHEN metric_key = 'daily_total_mileage_km'
+      THEN GREATEST(latest_total_mileage_km, VALUES(latest_total_mileage_km))
+    ELSE VALUES(metric_value)
+  END,
+  sample_count = sample_count + 1,
+  updated_at = CURRENT_TIMESTAMP
+`
+
+func floatField(env envelope.FrameEnvelope, key string) (float64, bool) {
+	if env.Fields == nil {
+		return 0, false
+	}
+	value, ok := env.Fields[key]
+	if !ok || value == nil {
+		return 0, false
+	}
+	switch typed := value.(type) {
+	case float64:
+		return typed, true
+	case float32:
+		return float64(typed), true
+	case int:
+		return float64(typed), true
+	case int64:
+		return float64(typed), true
+	case uint16:
+		return float64(typed), true
+	case uint32:
+		return float64(typed), true
+	case string:
+		parsed, err := strconv.ParseFloat(strings.TrimSpace(typed), 64)
+		return parsed, err == nil
+	default:
+		return 0, false
+	}
+}
diff --git a/go/vehicle-gateway/internal/stats/daily_metric_test.go b/go/vehicle-gateway/internal/stats/daily_metric_test.go
new file mode 100644
index 00000000..3ec011d7
--- /dev/null
+++ b/go/vehicle-gateway/internal/stats/daily_metric_test.go
@@ -0,0 +1,107 @@
+package stats
+
+import (
+	"context"
+	"database/sql"
+	"strings"
+	"testing"
+	"time"
+
+	"lingniu-vehicle-ingest/go/vehicle-gateway/internal/envelope"
+)
+
+func TestSamplesFromEnvelopeDerivesDailyMileageAndTotal(t *testing.T) {
+	loc := time.FixedZone("Asia/Shanghai", 8*3600)
+	env := envelope.FrameEnvelope{
+		Protocol:    envelope.ProtocolJT808,
+		VIN:         "LNBVIN00000000001",
+		EventTimeMS: time.Date(2026, 7, 1, 8, 30, 0, 0, loc).UnixMilli(),
+		Fields: map[string]any{
+			envelope.FieldTotalMileageKM: 10241.2,
+		},
+	}
+
+	samples, err := SamplesFromEnvelope(env, loc)
+	if err != nil {
+		t.Fatalf("SamplesFromEnvelope() error = %v", err)
+	}
+	if len(samples) != 2 {
+		t.Fatalf("sample count = %d", len(samples))
+	}
+	if samples[0].MetricKey != MetricDailyMileageKM || samples[0].MetricValue != 0 {
+		t.Fatalf("unexpected daily mileage sample: %#v", samples[0])
+	}
+	if samples[1].MetricKey != MetricDailyTotalMileageKM || samples[1].MetricValue != 10241.2 {
+		t.Fatalf("unexpected daily total sample: %#v", samples[1])
+	}
+	if samples[0].StatDate != "2026-07-01" {
+		t.Fatalf("stat date = %q", samples[0].StatDate)
+	}
+}
+
+func TestSamplesFromEnvelopeSkipsMissingVINOrMileage(t *testing.T) {
+	samples, err := SamplesFromEnvelope(envelope.FrameEnvelope{
+		Protocol: envelope.ProtocolJT808,
+		Fields:   map[string]any{envelope.FieldTotalMileageKM: 1.2},
+	}, nil)
+	if err != nil {
+		t.Fatalf("SamplesFromEnvelope() error = %v", err)
+	}
+	if len(samples) != 0 {
+		t.Fatalf("expected no samples without vin, got %#v", samples)
+	}
+
+	samples, err = SamplesFromEnvelope(envelope.FrameEnvelope{
+		Protocol: envelope.ProtocolGB32960,
+		VIN:      "LNBVIN00000000002",
+		Fields:   map[string]any{},
+	}, nil)
+	if err != nil {
+		t.Fatalf("SamplesFromEnvelope() error = %v", err)
+	}
+	if len(samples) != 0 {
+		t.Fatalf("expected no samples without mileage, got %#v", samples)
+	}
+}
+
+func TestWriterEnsuresSchemaAndUpsertsTwoMetrics(t *testing.T) {
+	exec := &recordingExec{}
+	writer := NewWriter(exec, time.FixedZone("Asia/Shanghai", 8*3600))
+	if err := writer.EnsureSchema(context.Background()); err != nil {
+		t.Fatalf("EnsureSchema() error = %v", err)
+	}
+	if err := writer.Append(context.Background(), envelope.FrameEnvelope{
+		Protocol:    envelope.ProtocolGB32960,
+		VIN:         "LNBVIN00000000002",
+		EventTimeMS: time.Date(2026, 7, 1, 9, 0, 0, 0, time.FixedZone("Asia/Shanghai", 8*3600)).UnixMilli(),
+		Fields: map[string]any{
+			envelope.FieldTotalMileageKM: "10000.0",
+		},
+	}); err != nil {
+		t.Fatalf("Append() error = %v", err)
+	}
+
+	if !strings.Contains(exec.calls[0].query, "CREATE TABLE IF NOT EXISTS vehicle_daily_metric") {
+		t.Fatalf("unexpected schema sql: %s", exec.calls[0].query)
+	}
+	if len(exec.calls) != 3 {
+		t.Fatalf("exec calls = %d", len(exec.calls))
+	}
+	if !strings.Contains(exec.calls[1].query, "ON DUPLICATE KEY UPDATE") {
+		t.Fatalf("unexpected upsert sql: %s", exec.calls[1].query)
+	}
+}
+
+type execCall struct {
+	query string
+	args  []any
+}
+
+type recordingExec struct {
+	calls []execCall
+}
+
+func (e *recordingExec) ExecContext(_ context.Context, query string, args ...any) (sql.Result, error) {
+	e.calls = append(e.calls, execCall{query: query, args: args})
+	return nil, nil
+}
diff --git a/go/vehicle-gateway/internal/stats/schema.go b/go/vehicle-gateway/internal/stats/schema.go
new file mode 100644
index 00000000..7bf860e8
--- /dev/null
+++ b/go/vehicle-gateway/internal/stats/schema.go
@@ -0,0 +1,20 @@
+package stats
+
+const DailyMetricTableSQL = `CREATE TABLE IF NOT EXISTS vehicle_daily_metric (
+  id BIGINT PRIMARY KEY AUTO_INCREMENT,
+  vin VARCHAR(32) NOT NULL,
+  stat_date DATE NOT NULL,
+  protocol VARCHAR(32) NOT NULL,
+  metric_key VARCHAR(64) NOT NULL,
+  metric_value DECIMAL(18,3) NOT NULL,
+  metric_unit VARCHAR(16) NOT NULL,
+  first_total_mileage_km DECIMAL(18,3) NULL,
+  latest_total_mileage_km DECIMAL(18,3) NULL,
+  sample_count BIGINT NOT NULL DEFAULT 0,
+  calculation_method VARCHAR(64) NOT NULL,
+  created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  updated_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
+  UNIQUE KEY uk_daily_metric (vin, stat_date, protocol, metric_key),
+  KEY idx_stat_date (stat_date),
+  KEY idx_protocol_metric (protocol, metric_key)
+)`