diff --git a/src/chongming_cli/gen_models.py b/src/chongming_cli/gen_models.py
index 6c5cabe..8f6cae8 100644
--- a/src/chongming_cli/gen_models.py
+++ b/src/chongming_cli/gen_models.py
@@ -17,7 +17,7 @@
 """
 
 import sys
-import json
+import orjson
 from pathlib import Path
 from typing import Any
 
@@ -163,7 +163,7 @@ def generate_pydantic_code(
                     if f.get("required", True):
                         if "default" in f:
                             default_repr = (
-                                json.dumps(f["default"])
+                                orjson.dumps(f["default"]).decode()
                                 if not isinstance(f["default"], str)
                                 else f"'{f['default']}'"
                             )
@@ -173,7 +173,7 @@ def generate_pydantic_code(
                     else:
                         if "default" in f:
                             default_repr = (
-                                json.dumps(f["default"])
+                                orjson.dumps(f["default"]).decode()
                                 if not isinstance(f["default"], str)
                                 else f"'{f['default']}'"
                             )