diff --git a/backend/internal/service/auth_oauth_email_flow.go b/backend/internal/service/auth_oauth_email_flow.go
index ca3403d4..4ab4e245 100644
--- a/backend/internal/service/auth_oauth_email_flow.go
+++ b/backend/internal/service/auth_oauth_email_flow.go
@@ -147,5 +147,11 @@ func (s *AuthService) ValidatePasswordCredentials(ctx context.Context, email, pa
 // RecordSuccessfulLogin updates last-login activity after a non-standard login
 // flow finishes with a real session.
 func (s *AuthService) RecordSuccessfulLogin(ctx context.Context, userID int64) {
+	if s != nil && s.userRepo != nil && userID > 0 {
+		user, err := s.userRepo.GetByID(ctx, userID)
+		if err == nil {
+			s.backfillEmailIdentityOnSuccessfulLogin(ctx, user)
+		}
+	}
 	s.touchUserLogin(ctx, userID)
 }
diff --git a/backend/internal/service/auth_service.go b/backend/internal/service/auth_service.go
index 40753139..dda6df04 100644
--- a/backend/internal/service/auth_service.go
+++ b/backend/internal/service/auth_service.go
@@ -430,6 +430,7 @@ func (s *AuthService) Login(ctx context.Context, email, password string) (string
 	if !user.IsActive() {
 		return "", nil, ErrUserNotActive
 	}
+	s.backfillEmailIdentityOnSuccessfulLogin(ctx, user)
 	s.touchUserLogin(ctx, user.ID)
 
 	// 生成JWT token
@@ -802,6 +803,13 @@ func (s *AuthService) touchUserLogin(ctx context.Context, userID int64) {
 	}
 }
 
+func (s *AuthService) backfillEmailIdentityOnSuccessfulLogin(ctx context.Context, user *User) {
+	if s == nil || user == nil || user.ID <= 0 {
+		return
+	}
+	s.ensureEmailAuthIdentity(ctx, user)
+}
+
 func (s *AuthService) ensureEmailAuthIdentity(ctx context.Context, user *User) {
 	if s == nil || s.entClient == nil || user == nil || user.ID <= 0 {
 		return
diff --git a/backend/internal/service/auth_service_identity_sync_test.go b/backend/internal/service/auth_service_identity_sync_test.go
index 5bd2b25d..fcb4813b 100644
--- a/backend/internal/service/auth_service_identity_sync_test.go
+++ b/backend/internal/service/auth_service_identity_sync_test.go
@@ -150,4 +150,41 @@ func TestAuthServiceLoginTouchesLastLoginAt(t *testing.T) {
 	require.NotNil(t, storedUser.LastActiveAt)
 	require.True(t, storedUser.LastLoginAt.After(old))
 	require.True(t, storedUser.LastActiveAt.After(old))
+
+	identity, err := client.AuthIdentity.Query().
+		Where(
+			authidentity.ProviderTypeEQ("email"),
+			authidentity.ProviderKeyEQ("email"),
+			authidentity.ProviderSubjectEQ("login@example.com"),
+		).
+		Only(ctx)
+	require.NoError(t, err)
+	require.Equal(t, user.ID, identity.UserID)
+}
+
+func TestAuthServiceRecordSuccessfulLoginBackfillsEmailIdentity(t *testing.T) {
+	svc, repo, client := newAuthServiceWithEnt(t)
+	ctx := context.Background()
+
+	user := &service.User{
+		Email:       "record@example.com",
+		Role:        service.RoleUser,
+		Status:      service.StatusActive,
+		Balance:     1,
+		Concurrency: 1,
+	}
+	require.NoError(t, user.SetPassword("password"))
+	require.NoError(t, repo.Create(ctx, user))
+
+	svc.RecordSuccessfulLogin(ctx, user.ID)
+
+	identity, err := client.AuthIdentity.Query().
+		Where(
+			authidentity.ProviderTypeEQ("email"),
+			authidentity.ProviderKeyEQ("email"),
+			authidentity.ProviderSubjectEQ("record@example.com"),
+		).
+		Only(ctx)
+	require.NoError(t, err)
+	require.Equal(t, user.ID, identity.UserID)
 }