diff --git a/agent/prompt_loader.py b/agent/prompt_loader.py
index ee77545..c828496 100644
--- a/agent/prompt_loader.py
+++ b/agent/prompt_loader.py
@@ -144,21 +144,23 @@ def replace_mcp_placeholders(mcp_settings: List[Dict], dataset_dir: str, bot_id:
     if not mcp_settings or not isinstance(mcp_settings, list):
         return mcp_settings
 
+    dataset_id_str = ','.join(dataset_ids) if dataset_ids else ''
+
     def replace_placeholders_in_obj(obj):
         """递归替换对象中的占位符"""
         if isinstance(obj, dict):
             for key, value in obj.items():
                 if key == 'args' and isinstance(value, list):
                     # 特别处理 args 列表
-                    obj[key] = [item.format(dataset_dir=dataset_dir, bot_id=bot_id, dataset_ids=','.join(dataset_ids)) if isinstance(item, str) else item
+                    obj[key] = [item.format(dataset_dir=dataset_dir, bot_id=bot_id, dataset_ids=dataset_id_str) if isinstance(item, str) else item
                                 for item in value]
                 elif isinstance(value, (dict, list)):
                     obj[key] = replace_placeholders_in_obj(value)
                 elif isinstance(value, str):
-                    obj[key] = value.format(dataset_dir=dataset_dir, bot_id=bot_id, dataset_ids=','.join(dataset_ids))
+                    obj[key] = value.format(dataset_dir=dataset_dir, bot_id=bot_id, dataset_ids=dataset_id_str)
         elif isinstance(obj, list):
             return [replace_placeholders_in_obj(item) if isinstance(item, (dict, list)) else 
-                    item.format(dataset_dir=dataset_dir, bot_id=bot_id, dataset_ids=','.join(dataset_ids)) if isinstance(item, str) else item
+                    item.format(dataset_dir=dataset_dir, bot_id=bot_id, dataset_ids=dataset_id_str) if isinstance(item, str) else item
                     for item in obj]
         return obj