diff --git a/apps/api/src/services/approval_db.py b/apps/api/src/services/approval_db.py
index c512aa9e..dc418e0c 100644
--- a/apps/api/src/services/approval_db.py
+++ b/apps/api/src/services/approval_db.py
@@ -171,8 +171,21 @@ class ApprovalDBService:
     資料庫授權服務 - 替代 in-memory TrustEngine
 
     所有操作皆為資料庫 CRUD，重啟後資料保持
+
+    Phase 16 R3.4: 支援 Repository 注入
+    - 有注入 repository: 使用 Repository 層
+    - 無注入: 使用內嵌 DB 操作 (向下相容)
     """
 
+    def __init__(self, repository=None):
+        """
+        初始化 ApprovalDBService
+
+        Args:
+            repository: IApprovalRepository 實例 (可選，Phase 16 DI)
+        """
+        self._repository = repository
+
     async def create_approval(
         self,
         request: ApprovalRequestCreate,
@@ -342,7 +355,14 @@ class ApprovalDBService:
     async def get_approval(self, approval_id: UUID) -> ApprovalRequest | None:
         """
         取得單一授權請求
+
+        Phase 16 R3.4: 支援 Repository 注入
         """
+        # Phase 16: 使用 Repository (如果有注入)
+        if self._repository:
+            return await self._repository.get_by_id(approval_id)
+
+        # Legacy: 內嵌 DB 操作
         async with get_db_context() as db:
             result = await db.execute(
                 select(ApprovalRecord).where(ApprovalRecord.id == str(approval_id))
@@ -357,7 +377,14 @@ class ApprovalDBService:
     async def get_pending_approvals(self) -> list[ApprovalRequest]:
         """
         取得所有待簽核請求
+
+        Phase 16 R3.4: 支援 Repository 注入
         """
+        # Phase 16: 使用 Repository (如果有注入)
+        if self._repository:
+            return await self._repository.get_pending()
+
+        # Legacy: 內嵌 DB 操作
         now = datetime.now(UTC)
 
         async with get_db_context() as db:
@@ -734,11 +761,25 @@ _approval_service: ApprovalDBService | None = None
 _timeline_service: TimelineDBService | None = None
 
 
-def get_approval_service() -> ApprovalDBService:
-    """取得授權服務實例"""
+def get_approval_service(use_repository: bool = False) -> ApprovalDBService:
+    """
+    取得授權服務實例
+
+    Args:
+        use_repository: 是否使用 Repository 層 (Phase 16 R3.4)
+
+    Phase 16: 絞殺者模式
+    - use_repository=False: 使用內嵌 DB 操作 (預設，向下相容)
+    - use_repository=True: 使用 ApprovalDBRepository
+    """
     global _approval_service
     if _approval_service is None:
-        _approval_service = ApprovalDBService()
+        if use_repository:
+            from src.repositories import get_approval_repository
+            _approval_service = ApprovalDBService(repository=get_approval_repository())
+            logger.info("approval_service_with_repository")
+        else:
+            _approval_service = ApprovalDBService()
     return _approval_service