diff --git a/backend/internal/handler/admin/account_handler.go b/backend/internal/handler/admin/account_handler.go
index 8dedcefd..f762511c 100644
--- a/backend/internal/handler/admin/account_handler.go
+++ b/backend/internal/handler/admin/account_handler.go
@@ -165,6 +165,8 @@ type AccountWithConcurrency struct {
 	CurrentRPM        *int     `json:"current_rpm,omitempty"`         // 当前分钟 RPM 计数
 }
 
+const accountListGroupUngroupedQueryValue = "ungrouped"
+
 func (h *AccountHandler) buildAccountResponseWithRuntime(ctx context.Context, account *service.Account) AccountWithConcurrency {
 	item := AccountWithConcurrency{
 		Account:            dto.AccountFromService(account),
@@ -226,7 +228,20 @@ func (h *AccountHandler) List(c *gin.Context) {
 
 	var groupID int64
 	if groupIDStr := c.Query("group"); groupIDStr != "" {
-		groupID, _ = strconv.ParseInt(groupIDStr, 10, 64)
+		if groupIDStr == accountListGroupUngroupedQueryValue {
+			groupID = service.AccountListGroupUngrouped
+		} else {
+			parsedGroupID, parseErr := strconv.ParseInt(groupIDStr, 10, 64)
+			if parseErr != nil {
+				response.ErrorFrom(c, infraerrors.BadRequest("INVALID_GROUP_FILTER", "invalid group filter"))
+				return
+			}
+			if parsedGroupID < 0 {
+				response.ErrorFrom(c, infraerrors.BadRequest("INVALID_GROUP_FILTER", "invalid group filter"))
+				return
+			}
+			groupID = parsedGroupID
+		}
 	}
 
 	accounts, total, err := h.adminService.ListAccounts(c.Request.Context(), page, pageSize, platform, accountType, status, search, groupID)
diff --git a/backend/internal/repository/account_repo.go b/backend/internal/repository/account_repo.go
index 7802cce0..35b908de 100644
--- a/backend/internal/repository/account_repo.go
+++ b/backend/internal/repository/account_repo.go
@@ -474,7 +474,9 @@ func (r *accountRepository) ListWithFilters(ctx context.Context, params paginati
 	if search != "" {
 		q = q.Where(dbaccount.NameContainsFold(search))
 	}
-	if groupID > 0 {
+	if groupID == service.AccountListGroupUngrouped {
+		q = q.Where(dbaccount.Not(dbaccount.HasAccountGroups()))
+	} else if groupID > 0 {
 		q = q.Where(dbaccount.HasAccountGroupsWith(dbaccountgroup.GroupIDEQ(groupID)))
 	}
 
diff --git a/backend/internal/repository/account_repo_integration_test.go b/backend/internal/repository/account_repo_integration_test.go
index e697802e..d6f0e337 100644
--- a/backend/internal/repository/account_repo_integration_test.go
+++ b/backend/internal/repository/account_repo_integration_test.go
@@ -214,6 +214,7 @@ func (s *AccountRepoSuite) TestListWithFilters() {
 		accType   string
 		status    string
 		search    string
+		groupID   int64
 		wantCount int
 		validate  func(accounts []service.Account)
 	}{
@@ -265,6 +266,21 @@ func (s *AccountRepoSuite) TestListWithFilters() {
 				s.Require().Contains(accounts[0].Name, "alpha")
 			},
 		},
+		{
+			name: "filter_by_ungrouped",
+			setup: func(client *dbent.Client) {
+				group := mustCreateGroup(s.T(), client, &service.Group{Name: "g-ungrouped"})
+				grouped := mustCreateAccount(s.T(), client, &service.Account{Name: "grouped-account"})
+				mustCreateAccount(s.T(), client, &service.Account{Name: "ungrouped-account"})
+				mustBindAccountToGroup(s.T(), client, grouped.ID, group.ID, 1)
+			},
+			groupID:   service.AccountListGroupUngrouped,
+			wantCount: 1,
+			validate: func(accounts []service.Account) {
+				s.Require().Equal("ungrouped-account", accounts[0].Name)
+				s.Require().Empty(accounts[0].GroupIDs)
+			},
+		},
 	}
 
 	for _, tt := range tests {
@@ -277,7 +293,7 @@ func (s *AccountRepoSuite) TestListWithFilters() {
 
 			tt.setup(client)
 
-			accounts, _, err := repo.ListWithFilters(ctx, pagination.PaginationParams{Page: 1, PageSize: 10}, tt.platform, tt.accType, tt.status, tt.search, 0)
+			accounts, _, err := repo.ListWithFilters(ctx, pagination.PaginationParams{Page: 1, PageSize: 10}, tt.platform, tt.accType, tt.status, tt.search, tt.groupID)
 			s.Require().NoError(err)
 			s.Require().Len(accounts, tt.wantCount)
 			if tt.validate != nil {
diff --git a/backend/internal/service/account_service.go b/backend/internal/service/account_service.go
index a06d8048..2e91db6b 100644
--- a/backend/internal/service/account_service.go
+++ b/backend/internal/service/account_service.go
@@ -14,6 +14,8 @@ var (
 	ErrAccountNilInput = infraerrors.BadRequest("ACCOUNT_NIL_INPUT", "account input cannot be nil")
 )
 
+const AccountListGroupUngrouped int64 = -1
+
 type AccountRepository interface {
 	Create(ctx context.Context, account *Account) error
 	GetByID(ctx context.Context, id int64) (*Account, error)
diff --git a/frontend/src/api/admin/accounts.ts b/frontend/src/api/admin/accounts.ts
index 9857de05..751da25f 100644
--- a/frontend/src/api/admin/accounts.ts
+++ b/frontend/src/api/admin/accounts.ts
@@ -66,6 +66,7 @@ export async function listWithEtag(
     platform?: string
     type?: string
     status?: string
+    group?: string
     search?: string
     lite?: string
   },
diff --git a/frontend/src/components/admin/account/AccountTableFilters.vue b/frontend/src/components/admin/account/AccountTableFilters.vue
index d8068336..a2a9ab04 100644
--- a/frontend/src/components/admin/account/AccountTableFilters.vue
+++ b/frontend/src/components/admin/account/AccountTableFilters.vue
@@ -26,5 +26,9 @@ const updateGroup = (value: string | number | boolean | null) => { emit('update:
 const pOpts = computed(() => [{ value: '', label: t('admin.accounts.allPlatforms') }, { value: 'anthropic', label: 'Anthropic' }, { value: 'openai', label: 'OpenAI' }, { value: 'gemini', label: 'Gemini' }, { value: 'antigravity', label: 'Antigravity' }, { value: 'sora', label: 'Sora' }])
 const tOpts = computed(() => [{ value: '', label: t('admin.accounts.allTypes') }, { value: 'oauth', label: t('admin.accounts.oauthType') }, { value: 'setup-token', label: t('admin.accounts.setupToken') }, { value: 'apikey', label: t('admin.accounts.apiKey') }, { value: 'bedrock', label: 'AWS Bedrock' }])
 const sOpts = computed(() => [{ value: '', label: t('admin.accounts.allStatus') }, { value: 'active', label: t('admin.accounts.status.active') }, { value: 'inactive', label: t('admin.accounts.status.inactive') }, { value: 'error', label: t('admin.accounts.status.error') }, { value: 'rate_limited', label: t('admin.accounts.status.rateLimited') }, { value: 'temp_unschedulable', label: t('admin.accounts.status.tempUnschedulable') }])
-const gOpts = computed(() => [{ value: '', label: t('admin.accounts.allGroups') }, ...(props.groups || []).map(g => ({ value: String(g.id), label: g.name }))])
+const gOpts = computed(() => [
+  { value: '', label: t('admin.accounts.allGroups') },
+  { value: 'ungrouped', label: t('admin.accounts.ungroupedGroup') },
+  ...(props.groups || []).map(g => ({ value: String(g.id), label: g.name }))
+])
 </script>
diff --git a/frontend/src/i18n/locales/en.ts b/frontend/src/i18n/locales/en.ts
index 6056e104..ba90e11a 100644
--- a/frontend/src/i18n/locales/en.ts
+++ b/frontend/src/i18n/locales/en.ts
@@ -1883,6 +1883,7 @@ export default {
       allTypes: 'All Types',
       allStatus: 'All Status',
       allGroups: 'All Groups',
+      ungroupedGroup: 'Ungrouped',
       oauthType: 'OAuth',
       setupToken: 'Setup Token',
       apiKey: 'API Key',
diff --git a/frontend/src/i18n/locales/zh.ts b/frontend/src/i18n/locales/zh.ts
index 602399b5..8180c568 100644
--- a/frontend/src/i18n/locales/zh.ts
+++ b/frontend/src/i18n/locales/zh.ts
@@ -1965,6 +1965,7 @@ export default {
       allTypes: '全部类型',
       allStatus: '全部状态',
       allGroups: '全部分组',
+      ungroupedGroup: '未分配分组',
       oauthType: 'OAuth',
       // Schedulable toggle
       schedulable: '参与调度',
diff --git a/frontend/src/views/admin/AccountsView.vue b/frontend/src/views/admin/AccountsView.vue
index 2ec5b47d..761e8403 100644
--- a/frontend/src/views/admin/AccountsView.vue
+++ b/frontend/src/views/admin/AccountsView.vue
@@ -758,6 +758,7 @@ const refreshAccountsIncrementally = async () => {
         platform?: string
         type?: string
         status?: string
+        group?: string
         search?: string
 
       },