diff --git a/api/app/services/knowledge_service.py b/api/app/services/knowledge_service.py
index b1d0d77b..56b630bb 100644
--- a/api/app/services/knowledge_service.py
+++ b/api/app/services/knowledge_service.py
@@ -7,7 +7,6 @@ from app.models.models_model import ModelConfig
 from app.schemas.knowledge_schema import KnowledgeCreate, KnowledgeUpdate
 from app.repositories import knowledge_repository
 from app.core.logging_config import get_business_logger
-from app.repositories.model_repository import ModelConfigRepository
 from app.models.models_model import ModelType
 
 business_logger = get_business_logger()
@@ -77,53 +76,55 @@ def create_knowledge(
 
         tenant_id = workspace.tenant_id
 
-        def _get_model_by_name_or_fallback(model_name: str | None, model_types: list, label: str):
-            """优先按 workspace 指定的 model name 查，找不到再 fallback 到 tenant 下第一个"""
-            if model_name:
+        def _get_model_by_id_or_fallback(model_id: str | None, model_types: list, label: str):
+            """优先按 workspace 绑定的 model_config id 查，找不到再 fallback 到 tenant 下最新创建的一个"""
+            if model_id:
                 model = db.query(ModelConfig).filter(
+                    ModelConfig.id == model_id,
                     ModelConfig.tenant_id == tenant_id,
-                    ModelConfig.name == model_name,
-                    ModelConfig.type.in_([t.value for t in model_types]),
                     ModelConfig.is_active == True,
                     ModelConfig.is_composite == False
                 ).first()
                 if model:
-                    business_logger.debug(f"Auto-bind {label} model from workspace default: {model.id} ({model_name})")
+                    business_logger.debug(f"Auto-bind {label} model from workspace default: {model.id}")
                     return model
-                business_logger.debug(f"Workspace default {label} model '{model_name}' not found, falling back to tenant")
-            models = ModelConfigRepository.get_by_type(db=db, model_types=model_types, tenant_id=tenant_id, is_active=True)
-            if models:
-                business_logger.debug(f"Auto-bind {label} model from tenant fallback: {models[0].id}")
-                return models[0]
-            return None
+                business_logger.debug(f"Workspace default {label} model id '{model_id}' not found, falling back to tenant latest")
+            model = db.query(ModelConfig).filter(
+                ModelConfig.tenant_id == tenant_id,
+                ModelConfig.type.in_([t.value for t in model_types]),
+                ModelConfig.is_active == True,
+                ModelConfig.is_composite == False
+            ).order_by(ModelConfig.created_at.desc()).first()
+            if model:
+                business_logger.debug(f"Auto-bind {label} model from tenant fallback (latest): {model.id}")
+            return model
 
         if not knowledge.embedding_id:
-            model = _get_model_by_name_or_fallback(workspace.embedding, [ModelType.EMBEDDING], "embedding")
+            model = _get_model_by_id_or_fallback(workspace.embedding, [ModelType.EMBEDDING], "embedding")
             if model:
                 knowledge.embedding_id = model.id
 
         if not knowledge.reranker_id:
-            model = _get_model_by_name_or_fallback(workspace.rerank, [ModelType.RERANK], "rerank")
+            model = _get_model_by_id_or_fallback(workspace.rerank, [ModelType.RERANK], "rerank")
             if model:
                 knowledge.reranker_id = model.id
 
         if not knowledge.llm_id:
-            model = _get_model_by_name_or_fallback(workspace.llm, [ModelType.LLM, ModelType.CHAT], "llm")
+            model = _get_model_by_id_or_fallback(workspace.llm, [ModelType.LLM, ModelType.CHAT], "llm")
             if model:
                 knowledge.llm_id = model.id
 
         if not knowledge.image2text_id:
-            image2text_models = db.query(ModelConfig).filter(
+            model = db.query(ModelConfig).filter(
                 ModelConfig.tenant_id == tenant_id,
                 ModelConfig.type.in_([ModelType.CHAT.value]),
                 ModelConfig.capability.contains(["vision"]),
                 ModelConfig.is_active == True,
                 ModelConfig.is_composite == False
-            ).order_by(ModelConfig.created_at.desc()).all()
-            if not image2text_models:
-                raise Exception("租户下没有可用的视觉模型，创建知识库失败")
-            knowledge.image2text_id = image2text_models[0].id
-            business_logger.debug(f"Auto-bind image2text model: {image2text_models[0].id}")
+            ).order_by(ModelConfig.created_at.desc()).first()
+            if model:
+                knowledge.image2text_id = model.id
+                business_logger.debug(f"Auto-bind image2text model: {model.id}")
 
         business_logger.debug(f"Start creating the knowledge base: {knowledge.name}")
         db_knowledge = knowledge_repository.create_knowledge(