diff --git a/httprunner/loader.py b/httprunner/loader.py
index 700f7582..d1e0d24f 100644
--- a/httprunner/loader.py
+++ b/httprunner/loader.py
@@ -179,7 +179,6 @@ def load_dot_env_file(dot_env_path):
 
             env_variables_mapping[variable.strip()] = value.strip()
 
-    utils.set_os_environ(env_variables_mapping)
     return env_variables_mapping
 
 
diff --git a/httprunner/parser.py b/httprunner/parser.py
index 481ddc9d..3d9f8a7d 100644
--- a/httprunner/parser.py
+++ b/httprunner/parser.py
@@ -618,6 +618,10 @@ def parse_tests(testcases, variables_mapping=None):
             }
         )
 
+        env_mapping = project_mapping["env"]
+        # set OS environment variables
+        utils.set_os_environ(env_mapping)
+
         # parse config parameters
         config_parameters = testcase_config.pop("parameters", [])
         cartesian_product_parameters_list = parse_parameters(
@@ -673,4 +677,7 @@ def parse_tests(testcases, variables_mapping=None):
             testcase_dict["config"]["functions"] = project_mapping["debugtalk"]["functions"]
             parsed_testcases_list.append(testcase_dict)
 
+        # unset OS environment variables
+        utils.unset_os_environ(env_mapping)
+
     return parsed_testcases_list
diff --git a/httprunner/utils.py b/httprunner/utils.py
index 4dbc6280..5ba9a161 100644
--- a/httprunner/utils.py
+++ b/httprunner/utils.py
@@ -26,7 +26,15 @@ def set_os_environ(variables_mapping):
     """
     for variable in variables_mapping:
         os.environ[variable] = variables_mapping[variable]
-        logger.log_debug("Loaded variable: {}".format(variable))
+        logger.log_debug("Set OS environment variable: {}".format(variable))
+
+
+def unset_os_environ(variables_mapping):
+    """ set variables mapping to os.environ
+    """
+    for variable in variables_mapping:
+        os.environ.pop(variable)
+        logger.log_debug("Unset OS environment variable: {}".format(variable))
 
 
 def query_json(json_content, query, delimiter='.'):
diff --git a/tests/debugtalk.py b/tests/debugtalk.py
index b44239de..4e22fa0f 100644
--- a/tests/debugtalk.py
+++ b/tests/debugtalk.py
@@ -7,7 +7,6 @@ import time
 from tests.api_server import HTTPBIN_SERVER, SECRET_KEY, gen_md5, get_sign
 
 BASE_URL = "http://127.0.0.1:5000"
-UserName = os.environ['UserName']
 
 
 demo_default_request = {
diff --git a/tests/test_loader.py b/tests/test_loader.py
index 104a855c..fc126873 100644
--- a/tests/test_loader.py
+++ b/tests/test_loader.py
@@ -565,7 +565,6 @@ class TestSuiteLoader(unittest.TestCase):
         path = os.path.join(
             os.getcwd(), 'tests/data/demo_locust.yml')
         locust_tests = loader.load_locust_tests(path)
-        self.assertEqual(locust_tests["config"]["variables"]["UserName"], "debugtalk")
         self.assertEqual(len(locust_tests["tests"]), 10)
         self.assertEqual(locust_tests["tests"][0][0]["name"], "index")
         self.assertEqual(locust_tests["tests"][9][0]["name"], "user-agent")