diff --git a/core/main_terminal_parts/context.py b/core/main_terminal_parts/context.py
index fa496e7..151e3d8 100644
--- a/core/main_terminal_parts/context.py
+++ b/core/main_terminal_parts/context.py
@@ -289,9 +289,11 @@ class MainTerminalContextMixin:
                         "role": conv["role"],
                         "content": conv["content"]
                     }
-                    reasoning = conv.get("reasoning_content")
-                    if reasoning:
-                        message["reasoning_content"] = reasoning
+                    # 对于思考模式（如 DeepSeek thinking），assistant 历史消息中的
+                    # reasoning_content 即使为空字符串也需要原样回传，否则下一轮可能被
+                    # API 判定为“未回传 reasoning_content”并返回 400。
+                    if "reasoning_content" in conv:
+                        message["reasoning_content"] = conv.get("reasoning_content", "")
                     # 如果有工具调用信息，添加到消息中
                     tool_calls = conv.get("tool_calls") or []
                     if tool_calls and self._tool_calls_followed_by_tools(conversation, idx, tool_calls):
diff --git a/server/chat_flow_task_main.py b/server/chat_flow_task_main.py
index 4088987..fa851a9 100644
--- a/server/chat_flow_task_main.py
+++ b/server/chat_flow_task_main.py
@@ -1200,10 +1200,10 @@ async def handle_task_with_sender(
         assistant_message = {
             "role": "assistant",
             "content": assistant_content,
-            "tool_calls": tool_calls
+            "tool_calls": tool_calls,
+            # thinking 模式下，reasoning_content 需要原样回传；即使该轮为空字符串也保留字段
+            "reasoning_content": current_thinking or "",
         }
-        if current_thinking:
-            assistant_message["reasoning_content"] = current_thinking
         
         messages.append(assistant_message)
         if assistant_content or current_thinking or tool_calls:
@@ -1211,7 +1211,7 @@ async def handle_task_with_sender(
                 "assistant",
                 assistant_content,
                 tool_calls=tool_calls if tool_calls else None,
-                reasoning_content=current_thinking or None
+                reasoning_content=current_thinking or ""
             )
         
         # 为下一轮迭代重置流状态标志，但保留 full_response 供上面保存使用