diff --git a/news/422.bugfix.md b/news/422.bugfix.md
new file mode 100644
index 0000000000..231c88a3d1
--- /dev/null
+++ b/news/422.bugfix.md
@@ -0,0 +1 @@
+Seek for other sitecustomize.py to import.
diff --git a/pdm/pep582/sitecustomize.py b/pdm/pep582/sitecustomize.py
index 24f4272915..921d84124a 100644
--- a/pdm/pep582/sitecustomize.py
+++ b/pdm/pep582/sitecustomize.py
@@ -41,11 +41,25 @@ def find_pypackage(path, version):
                 return result
 
 
-def main():
+def ensure_another_sitecustomize_imported():
+    import imp
+
+    try:
+        f, pathname, desc = imp.find_module("sitecustomize", sys.path)
+        try:
+            imp.load_module("another_sitecustomize", f, pathname, desc)
+        finally:
+            f.close()
+    except ImportError:
+        pass
+
 
+def main():
     self_path = os.path.normcase(os.path.dirname(os.path.abspath(__file__)))
     sys.path[:] = [path for path in sys.path if os.path.normcase(path) != self_path]
 
+    ensure_another_sitecustomize_imported()
+
     libpath = get_pypackages_path()
     if not libpath:
         return
diff --git a/tests/cli/test_run.py b/tests/cli/test_run.py
index 6ee382902b..95b8951b7f 100644
--- a/tests/cli/test_run.py
+++ b/tests/cli/test_run.py
@@ -1,3 +1,4 @@
+import functools
 import os
 import subprocess
 import textwrap
@@ -214,3 +215,40 @@ def test_run_with_another_project_root(project, invoke, capfd):
             assert ret.exit_code == 0
             out, _ = capfd.readouterr()
             assert out.strip() == "2.24.0"
+
+
+def test_import_another_sitecustomize(project, invoke, capfd):
+    project.meta["requires-python"] = ">=2.7"
+    project.write_pyproject()
+    # a script for checking another sitecustomize is imported
+    project.root.joinpath("foo.py").write_text(
+        textwrap.dedent(
+            """
+            import sys
+            module = sys.modules.get('another_sitecustomize')
+            if module:
+                print(module.__file__)
+            """
+        )
+    )
+    # ensure there have at least one sitecustomize can be imported
+    # there may have more than one sitecustomize.py in sys.path
+    project.root.joinpath("sitecustomize.py").write_text("# do nothing")
+    env = os.environ.copy()
+    paths = [str(project.root)]
+    original_paths = env.get("PYTHONPATH", "")
+    if original_paths:
+        paths.insert(0, original_paths)
+    env["PYTHONPATH"] = os.pathsep.join(paths)
+    # invoke pdm commands
+    invoke = functools.partial(invoke, env=env, obj=project)
+    project._environment = None
+    capfd.readouterr()
+    with cd(project.root):
+        invoke(["run", "python", "foo.py"])
+    # only the first and second sitecustomize module will be imported
+    # as sitecustomize and another_sitecustomize
+    # the first one is pdm.pep582.sitecustomize for sure
+    # the second one maybe not the dummy module injected here
+    out, _ = capfd.readouterr()
+    assert out.strip()
diff --git a/tests/conftest.py b/tests/conftest.py
index 71e5cfcddb..f0698fd10f 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -224,6 +224,13 @@ def pip_global_tempdir_manager():
         yield
 
 
+def remove_pep582_path_from_pythonpath(pythonpath):
+    """Remove all pep582 paths of PDM from PYTHONPATH"""
+    paths = pythonpath.split(os.pathsep)
+    paths = [path for path in paths if "pdm/pep582" not in path]
+    return os.pathsep.join(paths)
+
+
 @pytest.fixture()
 def project_no_init(tmp_path, mocker):
     p = main.create_project(tmp_path)
@@ -235,8 +242,11 @@ def project_no_init(tmp_path, mocker):
     do_use(p, getattr(sys, "_base_executable", sys.executable))
     with temp_environ():
         os.environ.pop("VIRTUAL_ENV", None)
-        os.environ.pop("PYTHONPATH", None)
         os.environ.pop("PEP582_PACKAGES", None)
+        pythonpath = os.environ.pop("PYTHONPATH", "")
+        pythonpath = remove_pep582_path_from_pythonpath(pythonpath)
+        if pythonpath:
+            os.environ["PYTHONPATH"] = pythonpath
         yield p
     # Restore the config items
     Config._config_map = old_config_map