diff --git a/mmengine/config/config.py b/mmengine/config/config.py
index 4645aafede..29e71a671e 100644
--- a/mmengine/config/config.py
+++ b/mmengine/config/config.py
@@ -335,18 +335,20 @@ def _substitute_environment_vars(filename: str, temp_config_name: str):
         """
         with open(filename, encoding='utf-8') as f:
             config_file = f.read()
-        regexp = r'\{\{[\'\"]?\s*\$(\w+)\s*\:?\s*(\S*?)\s*[\'\"]?\}\}'
+        regexp = r'\{\{[\'\"]?\s*\$(\w+)\s*\:\s*(\S*?)\s*[\'\"]?\}\}'
         keys = re.findall(regexp, config_file)
         env_variables = dict()
         for var_name, value in keys:
-            regexp = r'\{\{[\'\"]?\s*\$' + var_name + r'\s*\:?\s*' \
+            regexp = r'\{\{[\'\"]?\s*\$' + var_name + r'\s*\:\s*' \
                 + value + r'\s*[\'\"]?\}\}'
             if var_name in os.environ:
                 value = os.environ[var_name]
                 env_variables[var_name] = value
-                print_log(f'Using env variable `{var_name}` with value of '
-                          f'{value} to replace item in config.')
-            elif not value:
+                print_log(
+                    f'Using env variable `{var_name}` with value of '
+                    f'{value} to replace item in config.',
+                    logger='current')
+            if not value:
                 raise KeyError(f'`{var_name}` cannot be found in `os.environ`.'
                                f' Please set `{var_name}` in environment or '
                                'give a default value.')
diff --git a/tests/data/config/py_config/test_environment_var.py b/tests/data/config/py_config/test_environment_var.py
index 86697d7c05..89508fb133 100644
--- a/tests/data/config/py_config/test_environment_var.py
+++ b/tests/data/config/py_config/test_environment_var.py
@@ -1,4 +1,4 @@
 # Copyright (c) OpenMMLab. All rights reserved.
-item1 = '{{ $ITEM1 }}'
+item1 = '{{ $ITEM1: }}'
 item2 = '{{ $ITEM2:default_value }}'
 item3 = {{' $ITEM3:80 '}}
diff --git a/tests/test_config/test_config.py b/tests/test_config/test_config.py
index f1784e9740..51a7afe97c 100644
--- a/tests/test_config/test_config.py
+++ b/tests/test_config/test_config.py
@@ -370,7 +370,7 @@ def test_substitute_environment_vars(self, tmp_path):
         cfg = tmp_path / 'tmp_cfg1.py'
         substituted_cfg = tmp_path / 'tmp_cfg2.py'
 
-        cfg_text = 'a={{$A}}\n'
+        cfg_text = 'a={{$A:}}\n'
         with open(cfg, 'w') as f:
             f.write(cfg_text)
         with pytest.raises(KeyError):