diff --git a/backend/internal/service/admin_group.go b/backend/internal/service/admin_group.go
index fd28f681cb..d719e4d501 100644
--- a/backend/internal/service/admin_group.go
+++ b/backend/internal/service/admin_group.go
@@ -469,7 +469,7 @@ func (s *adminServiceImpl) CreateGroup(ctx context.Context, input *CreateGroupIn
 	// 先归一化（非订阅分组清空高峰配置、清洗停用状态下的脏字段）再校验，与 UpdateGroup 同一收口。
 	peakRateEnabled, peakStart, peakEnd, peakRateMultiplier := NormalizePeakRateConfig(subscriptionType, input.PeakRateEnabled, input.PeakStart, input.PeakEnd, peakRateMultiplier)
 	if err := ValidatePeakRateConfig(subscriptionType, peakRateEnabled, peakStart, peakEnd, peakRateMultiplier); err != nil {
-		return nil, err
+		return nil, infraerrors.BadRequest("INVALID_PEAK_RATE_CONFIG", err.Error())
 	}
 
 	profitMinMargin := 0.0
@@ -867,7 +867,7 @@ func (s *adminServiceImpl) UpdateGroup(ctx context.Context, id int64, input *Upd
 	// 防止单独修改 start/end 导致最终 start>=end 等非法配置入库。与 CreateGroup 同一收口。
 	group.PeakRateEnabled, group.PeakStart, group.PeakEnd, group.PeakRateMultiplier = NormalizePeakRateConfig(group.SubscriptionType, group.PeakRateEnabled, group.PeakStart, group.PeakEnd, group.PeakRateMultiplier)
 	if err := ValidatePeakRateConfig(group.SubscriptionType, group.PeakRateEnabled, group.PeakStart, group.PeakEnd, group.PeakRateMultiplier); err != nil {
-		return nil, err
+		return nil, infraerrors.BadRequest("INVALID_PEAK_RATE_CONFIG", err.Error())
 	}
 	if input.ProfitControlEnabled != nil {
 		group.ProfitControlEnabled = *input.ProfitControlEnabled
diff --git a/backend/internal/service/admin_service_group_test.go b/backend/internal/service/admin_service_group_test.go
index 7d5774d794..1f7a71f9f3 100644
--- a/backend/internal/service/admin_service_group_test.go
+++ b/backend/internal/service/admin_service_group_test.go
@@ -1145,6 +1145,66 @@ func TestAdminService_UpdateGroup_ClearsReasoningPolicyForUnsupportedPlatform(t
 	require.Empty(t, repo.updated.ReasoningEffortMappings)
 }
 
+func TestAdminService_CreateGroup_InvalidPeakRateReturnsBadRequest(t *testing.T) {
+	repo := &groupRepoStubForAdmin{}
+	svc := &adminServiceImpl{groupRepo: repo}
+
+	_, err := svc.CreateGroup(context.Background(), &CreateGroupInput{
+		Name:             "subscription-group",
+		Platform:         PlatformOpenAI,
+		SubscriptionType: SubscriptionTypeSubscription,
+		PeakRateEnabled:  true,
+		PeakStart:        "20:00",
+		PeakEnd:          "08:30",
+	})
+
+	require.ErrorContains(t, err, "peak_end")
+	require.Equal(t, http.StatusBadRequest, infraerrors.Code(err))
+	require.Equal(t, "INVALID_PEAK_RATE_CONFIG", infraerrors.Reason(err))
+	require.Nil(t, repo.created)
+}
+
+func TestAdminService_UpdateGroup_PeakRateValidation(t *testing.T) {
+	tests := []struct {
+		name    string
+		input   UpdateGroupInput
+		wantErr bool
+	}{
+		{"cross-day window", UpdateGroupInput{PeakStart: ptrString("20:00"), PeakEnd: ptrString("08:30")}, true},
+		{"partial update invalidates window", UpdateGroupInput{PeakEnd: ptrString("08:30")}, true},
+		{"partial update keeps valid window", UpdateGroupInput{PeakEnd: ptrString("19:00")}, false},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			repo := &groupRepoStubForAdmin{getByID: &Group{
+				ID:                 1,
+				Name:               "subscription-group",
+				Platform:           PlatformOpenAI,
+				Status:             StatusActive,
+				SubscriptionType:   SubscriptionTypeSubscription,
+				PeakRateEnabled:    true,
+				PeakStart:          "14:00",
+				PeakEnd:            "18:00",
+				PeakRateMultiplier: 3,
+			}}
+			svc := &adminServiceImpl{groupRepo: repo}
+
+			_, err := svc.UpdateGroup(context.Background(), 1, &tt.input)
+
+			if tt.wantErr {
+				require.ErrorContains(t, err, "peak_end")
+				require.Equal(t, http.StatusBadRequest, infraerrors.Code(err))
+				require.Equal(t, "INVALID_PEAK_RATE_CONFIG", infraerrors.Reason(err))
+				require.Nil(t, repo.updated)
+			} else {
+				require.NoError(t, err)
+				require.NotNil(t, repo.updated)
+				require.Equal(t, "19:00", repo.updated.PeakEnd)
+			}
+		})
+	}
+}
+
 func TestAdminService_UpdateGroup_ClearsPeakRateWhenChangingToStandard(t *testing.T) {
 	existingGroup := &Group{
 		ID:                 1,