diff --git a/data_juicer/core/tracer.py b/data_juicer/core/tracer.py
index 03926b785d..c0bbd18d1b 100644
--- a/data_juicer/core/tracer.py
+++ b/data_juicer/core/tracer.py
@@ -65,7 +65,7 @@ def trace_mapper(self, op_name: str, previous_ds: Dataset, processed_ds: Dataset
             if previous_sample != processed_sample:
                 dif_dict.append(
                     {
-                        "original text": previous_sample,
+                        "original_text": previous_sample,
                         "processed_text": processed_sample,
                     }
                 )
diff --git a/tests/core/test_tracer.py b/tests/core/test_tracer.py
index 7bd9a51e57..58bce2a03a 100644
--- a/tests/core/test_tracer.py
+++ b/tests/core/test_tracer.py
@@ -30,7 +30,7 @@ def test_trace_mapper(self):
         ])
         dif_list = [
             {
-                'original text': 'text 2',
+                'original_text': 'text 2',
                 'processed_text': 'processed text 2',
             }
         ]
@@ -57,7 +57,7 @@ def test_trace_mapper_less_show_num(self):
         ])
         dif_list = [
             {
-                'original text': 'text 2',
+                'original_text': 'text 2',
                 'processed_text': 'processed text 2',
             }
         ]