diff --git a/config/config.yaml b/config/config.yaml
index 17339eda5..444f55efd 100644
--- a/config/config.yaml
+++ b/config/config.yaml
@@ -84,4 +84,4 @@ MODEL_FOR_RESEARCHER_REPORT: gpt-3.5-turbo-16k
 ### browser path for pyppeteer engine, support Chrome, Chromium,MS Edge
 #PYPPETEER_EXECUTABLE_PATH: "/usr/bin/google-chrome-stable"
 
-PROMPT_FORMAT: markdown #json or markdown
\ No newline at end of file
+PROMPT_FORMAT: json #json or markdown
\ No newline at end of file
diff --git a/metagpt/actions/action.py b/metagpt/actions/action.py
index c688f6661..790295d55 100644
--- a/metagpt/actions/action.py
+++ b/metagpt/actions/action.py
@@ -12,7 +12,6 @@ from typing import Optional
 from tenacity import retry, stop_after_attempt, wait_fixed
 
 from metagpt.actions.action_output import ActionOutput
-from metagpt.config import CONFIG
 from metagpt.llm import LLM
 from metagpt.logs import logger
 from metagpt.utils.common import OutputParser
@@ -57,7 +56,7 @@ class Action(ABC):
         output_class_name: str,
         output_data_mapping: dict,
         system_msgs: Optional[list[str]] = None,
-        format=CONFIG.prompt_format,
+        format="markdown",  # compatible to original format
     ) -> ActionOutput:
         """Append default prefix"""
         if not system_msgs: