diff --git a/backend/internal/repository/user_subscription_repo.go b/backend/internal/repository/user_subscription_repo.go
index 2b308674..cd3b9db6 100644
--- a/backend/internal/repository/user_subscription_repo.go
+++ b/backend/internal/repository/user_subscription_repo.go
@@ -291,13 +291,11 @@ func (r *userSubscriptionRepository) ResetMonthlyUsage(ctx context.Context, id i
 	return translatePersistenceError(err, service.ErrSubscriptionNotFound, nil)
 }
 
-// IncrementUsage 原子性地累加用量并校验限额。
-// 使用单条 SQL 语句同时检查 Group 的限额，如果任一限额即将超出则拒绝更新。
-// 当更新失败时，会执行额外查询确定具体超出的限额类型。
+// IncrementUsage 原子性地累加订阅用量。
+// 限额检查已在请求前由 BillingCacheService.CheckBillingEligibility 完成，
+// 此处仅负责记录实际消费，确保消费数据的完整性。
 func (r *userSubscriptionRepository) IncrementUsage(ctx context.Context, id int64, costUSD float64) error {
-	// 使用 JOIN 的原子更新：只有当所有限额条件满足时才执行累加
-	// NULL 限额表示无限制
-	const atomicUpdateSQL = `
+	const updateSQL = `
 		UPDATE user_subscriptions us
 		SET
 			daily_usage_usd = us.daily_usage_usd + $1,
@@ -309,13 +307,10 @@ func (r *userSubscriptionRepository) IncrementUsage(ctx context.Context, id int6
 			AND us.deleted_at IS NULL
 			AND us.group_id = g.id
 			AND g.deleted_at IS NULL
-			AND (g.daily_limit_usd IS NULL OR us.daily_usage_usd + $1 <= g.daily_limit_usd)
-			AND (g.weekly_limit_usd IS NULL OR us.weekly_usage_usd + $1 <= g.weekly_limit_usd)
-			AND (g.monthly_limit_usd IS NULL OR us.monthly_usage_usd + $1 <= g.monthly_limit_usd)
 	`
 
 	client := clientFromContext(ctx, r.client)
-	result, err := client.ExecContext(ctx, atomicUpdateSQL, costUSD, id)
+	result, err := client.ExecContext(ctx, updateSQL, costUSD, id)
 	if err != nil {
 		return err
 	}
@@ -326,64 +321,11 @@ func (r *userSubscriptionRepository) IncrementUsage(ctx context.Context, id int6
 	}
 
 	if affected > 0 {
-		return nil // 更新成功
+		return nil
 	}
 
-	// affected == 0：可能是订阅不存在、分组已删除、或限额超出
-	// 执行额外查询确定具体原因
-	return r.checkIncrementFailureReason(ctx, id, costUSD)
-}
-
-// checkIncrementFailureReason 查询更新失败的具体原因
-func (r *userSubscriptionRepository) checkIncrementFailureReason(ctx context.Context, id int64, costUSD float64) error {
-	const checkSQL = `
-		SELECT
-			CASE WHEN us.deleted_at IS NOT NULL THEN 'subscription_deleted'
-			     WHEN g.id IS NULL THEN 'subscription_not_found'
-			     WHEN g.deleted_at IS NOT NULL THEN 'group_deleted'
-			     WHEN g.daily_limit_usd IS NOT NULL AND us.daily_usage_usd + $1 > g.daily_limit_usd THEN 'daily_exceeded'
-			     WHEN g.weekly_limit_usd IS NOT NULL AND us.weekly_usage_usd + $1 > g.weekly_limit_usd THEN 'weekly_exceeded'
-			     WHEN g.monthly_limit_usd IS NOT NULL AND us.monthly_usage_usd + $1 > g.monthly_limit_usd THEN 'monthly_exceeded'
-			     ELSE 'unknown'
-			END AS reason
-		FROM user_subscriptions us
-		LEFT JOIN groups g ON us.group_id = g.id
-		WHERE us.id = $2
-	`
-
-	client := clientFromContext(ctx, r.client)
-	rows, err := client.QueryContext(ctx, checkSQL, costUSD, id)
-	if err != nil {
-		return err
-	}
-	defer func() { _ = rows.Close() }()
-
-	if !rows.Next() {
-		return service.ErrSubscriptionNotFound
-	}
-
-	var reason string
-	if err := rows.Scan(&reason); err != nil {
-		return err
-	}
-
-	if err := rows.Err(); err != nil {
-		return err
-	}
-
-	switch reason {
-	case "subscription_not_found", "subscription_deleted", "group_deleted":
-		return service.ErrSubscriptionNotFound
-	case "daily_exceeded":
-		return service.ErrDailyLimitExceeded
-	case "weekly_exceeded":
-		return service.ErrWeeklyLimitExceeded
-	case "monthly_exceeded":
-		return service.ErrMonthlyLimitExceeded
-	default:
-		// unknown 情况理论上不应发生，但作为兜底返回
-		return service.ErrSubscriptionNotFound
-	}
+	// affected == 0：订阅不存在或已删除
+	return service.ErrSubscriptionNotFound
 }
 
 func (r *userSubscriptionRepository) BatchUpdateExpiredStatus(ctx context.Context) (int64, error) {
diff --git a/backend/internal/repository/user_subscription_repo_integration_test.go b/backend/internal/repository/user_subscription_repo_integration_test.go
index 3a6c6434..2099e5d8 100644
--- a/backend/internal/repository/user_subscription_repo_integration_test.go
+++ b/backend/internal/repository/user_subscription_repo_integration_test.go
@@ -633,112 +633,7 @@ func (s *UserSubscriptionRepoSuite) TestActiveExpiredBoundaries_UsageAndReset_Ba
 	s.Require().Equal(service.SubscriptionStatusExpired, updated.Status, "expected status expired")
 }
 
-// --- 限额检查与软删除过滤测试 ---
-
-func (s *UserSubscriptionRepoSuite) mustCreateGroupWithLimits(name string, daily, weekly, monthly *float64) *service.Group {
-	s.T().Helper()
-
-	create := s.client.Group.Create().
-		SetName(name).
-		SetStatus(service.StatusActive).
-		SetSubscriptionType(service.SubscriptionTypeSubscription)
-
-	if daily != nil {
-		create.SetDailyLimitUsd(*daily)
-	}
-	if weekly != nil {
-		create.SetWeeklyLimitUsd(*weekly)
-	}
-	if monthly != nil {
-		create.SetMonthlyLimitUsd(*monthly)
-	}
-
-	g, err := create.Save(s.ctx)
-	s.Require().NoError(err, "create group with limits")
-	return groupEntityToService(g)
-}
-
-func (s *UserSubscriptionRepoSuite) TestIncrementUsage_DailyLimitExceeded() {
-	user := s.mustCreateUser("dailylimit@test.com", service.RoleUser)
-	dailyLimit := 10.0
-	group := s.mustCreateGroupWithLimits("g-dailylimit", &dailyLimit, nil, nil)
-	sub := s.mustCreateSubscription(user.ID, group.ID, nil)
-
-	// 先增加 9.0，应该成功
-	err := s.repo.IncrementUsage(s.ctx, sub.ID, 9.0)
-	s.Require().NoError(err, "first increment should succeed")
-
-	// 再增加 2.0，会超过 10.0 限额，应该失败
-	err = s.repo.IncrementUsage(s.ctx, sub.ID, 2.0)
-	s.Require().Error(err, "should fail when daily limit exceeded")
-	s.Require().ErrorIs(err, service.ErrDailyLimitExceeded)
-
-	// 验证用量没有变化
-	got, err := s.repo.GetByID(s.ctx, sub.ID)
-	s.Require().NoError(err)
-	s.Require().InDelta(9.0, got.DailyUsageUSD, 1e-6, "usage should not change after failed increment")
-}
-
-func (s *UserSubscriptionRepoSuite) TestIncrementUsage_WeeklyLimitExceeded() {
-	user := s.mustCreateUser("weeklylimit@test.com", service.RoleUser)
-	weeklyLimit := 50.0
-	group := s.mustCreateGroupWithLimits("g-weeklylimit", nil, &weeklyLimit, nil)
-	sub := s.mustCreateSubscription(user.ID, group.ID, nil)
-
-	// 增加 45.0，应该成功
-	err := s.repo.IncrementUsage(s.ctx, sub.ID, 45.0)
-	s.Require().NoError(err, "first increment should succeed")
-
-	// 再增加 10.0，会超过 50.0 限额，应该失败
-	err = s.repo.IncrementUsage(s.ctx, sub.ID, 10.0)
-	s.Require().Error(err, "should fail when weekly limit exceeded")
-	s.Require().ErrorIs(err, service.ErrWeeklyLimitExceeded)
-}
-
-func (s *UserSubscriptionRepoSuite) TestIncrementUsage_MonthlyLimitExceeded() {
-	user := s.mustCreateUser("monthlylimit@test.com", service.RoleUser)
-	monthlyLimit := 100.0
-	group := s.mustCreateGroupWithLimits("g-monthlylimit", nil, nil, &monthlyLimit)
-	sub := s.mustCreateSubscription(user.ID, group.ID, nil)
-
-	// 增加 90.0，应该成功
-	err := s.repo.IncrementUsage(s.ctx, sub.ID, 90.0)
-	s.Require().NoError(err, "first increment should succeed")
-
-	// 再增加 20.0，会超过 100.0 限额，应该失败
-	err = s.repo.IncrementUsage(s.ctx, sub.ID, 20.0)
-	s.Require().Error(err, "should fail when monthly limit exceeded")
-	s.Require().ErrorIs(err, service.ErrMonthlyLimitExceeded)
-}
-
-func (s *UserSubscriptionRepoSuite) TestIncrementUsage_NoLimits() {
-	user := s.mustCreateUser("nolimits@test.com", service.RoleUser)
-	group := s.mustCreateGroupWithLimits("g-nolimits", nil, nil, nil) // 无限额
-	sub := s.mustCreateSubscription(user.ID, group.ID, nil)
-
-	// 应该可以增加任意金额
-	err := s.repo.IncrementUsage(s.ctx, sub.ID, 1000000.0)
-	s.Require().NoError(err, "should succeed without limits")
-
-	got, err := s.repo.GetByID(s.ctx, sub.ID)
-	s.Require().NoError(err)
-	s.Require().InDelta(1000000.0, got.DailyUsageUSD, 1e-6)
-}
-
-func (s *UserSubscriptionRepoSuite) TestIncrementUsage_AtExactLimit() {
-	user := s.mustCreateUser("exactlimit@test.com", service.RoleUser)
-	dailyLimit := 10.0
-	group := s.mustCreateGroupWithLimits("g-exactlimit", &dailyLimit, nil, nil)
-	sub := s.mustCreateSubscription(user.ID, group.ID, nil)
-
-	// 正好达到限额应该成功
-	err := s.repo.IncrementUsage(s.ctx, sub.ID, 10.0)
-	s.Require().NoError(err, "should succeed at exact limit")
-
-	got, err := s.repo.GetByID(s.ctx, sub.ID)
-	s.Require().NoError(err)
-	s.Require().InDelta(10.0, got.DailyUsageUSD, 1e-6)
-}
+// --- 软删除过滤测试 ---
 
 func (s *UserSubscriptionRepoSuite) TestIncrementUsage_SoftDeletedGroup() {
 	user := s.mustCreateUser("softdeleted@test.com", service.RoleUser)
@@ -779,7 +674,7 @@ func (s *UserSubscriptionRepoSuite) TestUpdate_NilInput() {
 
 func (s *UserSubscriptionRepoSuite) TestIncrementUsage_Concurrent() {
 	user := s.mustCreateUser("concurrent@test.com", service.RoleUser)
-	group := s.mustCreateGroupWithLimits("g-concurrent", nil, nil, nil) // 无限额
+	group := s.mustCreateGroup("g-concurrent")
 	sub := s.mustCreateSubscription(user.ID, group.ID, nil)
 
 	const numGoroutines = 10
@@ -808,34 +703,6 @@ func (s *UserSubscriptionRepoSuite) TestIncrementUsage_Concurrent() {
 	s.Require().InDelta(expectedUsage, got.MonthlyUsageUSD, 1e-6, "monthly usage should be correctly accumulated")
 }
 
-func (s *UserSubscriptionRepoSuite) TestIncrementUsage_ConcurrentWithLimit() {
-	user := s.mustCreateUser("concurrentlimit@test.com", service.RoleUser)
-	dailyLimit := 5.0
-	group := s.mustCreateGroupWithLimits("g-concurrentlimit", &dailyLimit, nil, nil)
-	sub := s.mustCreateSubscription(user.ID, group.ID, nil)
-
-	// 注意：事务内的操作是串行的，所以这里改为顺序执行以验证限额逻辑
-	// 尝试增加 10 次，每次 1.0，但限额只有 5.0
-	const numAttempts = 10
-	const incrementPerAttempt = 1.0
-
-	successCount := 0
-	for i := 0; i < numAttempts; i++ {
-		err := s.repo.IncrementUsage(s.ctx, sub.ID, incrementPerAttempt)
-		if err == nil {
-			successCount++
-		}
-	}
-
-	// 验证：应该有 5 次成功（不超过限额），5 次失败（超出限额）
-	s.Require().Equal(5, successCount, "exactly 5 increments should succeed (limit=5, increment=1)")
-
-	// 验证最终用量等于限额
-	got, err := s.repo.GetByID(s.ctx, sub.ID)
-	s.Require().NoError(err)
-	s.Require().InDelta(dailyLimit, got.DailyUsageUSD, 1e-6, "daily usage should equal limit")
-}
-
 func (s *UserSubscriptionRepoSuite) TestTxContext_RollbackIsolation() {
 	baseClient := testEntClient(s.T())
 	tx, err := baseClient.Tx(context.Background())
diff --git a/backend/internal/service/admin_service.go b/backend/internal/service/admin_service.go
index 4be09810..feeb19a0 100644
--- a/backend/internal/service/admin_service.go
+++ b/backend/internal/service/admin_service.go
@@ -488,6 +488,11 @@ func (s *adminServiceImpl) CreateGroup(ctx context.Context, input *CreateGroupIn
 		subscriptionType = SubscriptionTypeStandard
 	}
 
+	// 限额字段：0 和 nil 都表示"无限制"
+	dailyLimit := normalizeLimit(input.DailyLimitUSD)
+	weeklyLimit := normalizeLimit(input.WeeklyLimitUSD)
+	monthlyLimit := normalizeLimit(input.MonthlyLimitUSD)
+
 	group := &Group{
 		Name:             input.Name,
 		Description:      input.Description,
@@ -496,9 +501,9 @@ func (s *adminServiceImpl) CreateGroup(ctx context.Context, input *CreateGroupIn
 		IsExclusive:      input.IsExclusive,
 		Status:           StatusActive,
 		SubscriptionType: subscriptionType,
-		DailyLimitUSD:    input.DailyLimitUSD,
-		WeeklyLimitUSD:   input.WeeklyLimitUSD,
-		MonthlyLimitUSD:  input.MonthlyLimitUSD,
+		DailyLimitUSD:    dailyLimit,
+		WeeklyLimitUSD:   weeklyLimit,
+		MonthlyLimitUSD:  monthlyLimit,
 	}
 	if err := s.groupRepo.Create(ctx, group); err != nil {
 		return nil, err
@@ -506,6 +511,14 @@ func (s *adminServiceImpl) CreateGroup(ctx context.Context, input *CreateGroupIn
 	return group, nil
 }
 
+// normalizeLimit 将 0 或负数转换为 nil（表示无限制）
+func normalizeLimit(limit *float64) *float64 {
+	if limit == nil || *limit <= 0 {
+		return nil
+	}
+	return limit
+}
+
 func (s *adminServiceImpl) UpdateGroup(ctx context.Context, id int64, input *UpdateGroupInput) (*Group, error) {
 	group, err := s.groupRepo.GetByID(ctx, id)
 	if err != nil {
@@ -535,15 +548,15 @@ func (s *adminServiceImpl) UpdateGroup(ctx context.Context, id int64, input *Upd
 	if input.SubscriptionType != "" {
 		group.SubscriptionType = input.SubscriptionType
 	}
-	// 限额字段支持设置为nil（清除限额）或具体值
+	// 限额字段：0 和 nil 都表示"无限制"，正数表示具体限额
 	if input.DailyLimitUSD != nil {
-		group.DailyLimitUSD = input.DailyLimitUSD
+		group.DailyLimitUSD = normalizeLimit(input.DailyLimitUSD)
 	}
 	if input.WeeklyLimitUSD != nil {
-		group.WeeklyLimitUSD = input.WeeklyLimitUSD
+		group.WeeklyLimitUSD = normalizeLimit(input.WeeklyLimitUSD)
 	}
 	if input.MonthlyLimitUSD != nil {
-		group.MonthlyLimitUSD = input.MonthlyLimitUSD
+		group.MonthlyLimitUSD = normalizeLimit(input.MonthlyLimitUSD)
 	}
 
 	if err := s.groupRepo.Update(ctx, group); err != nil {
diff --git a/backend/internal/service/subscription_service.go b/backend/internal/service/subscription_service.go
index 09554c0f..f6aefb83 100644
--- a/backend/internal/service/subscription_service.go
+++ b/backend/internal/service/subscription_service.go
@@ -490,6 +490,7 @@ func (s *SubscriptionService) CheckAndResetWindows(ctx context.Context, sub *Use
 }
 
 // CheckUsageLimits 检查使用限额（返回错误如果超限）
+// 用于中间件的快速预检查，additionalCost 通常为 0
 func (s *SubscriptionService) CheckUsageLimits(ctx context.Context, sub *UserSubscription, group *Group, additionalCost float64) error {
 	if !sub.CheckDailyLimit(group, additionalCost) {
 		return ErrDailyLimitExceeded