diff --git a/.chronus/changes/fix-python-constant-query-2025-9-24-14-46-59.md b/.chronus/changes/fix-python-constant-query-2025-9-24-14-46-59.md
new file mode 100644
index 00000000000..d3ccaa467ec
--- /dev/null
+++ b/.chronus/changes/fix-python-constant-query-2025-9-24-14-46-59.md
@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/http-client-python"
+---
+
+Fix runtime error for constant query parameter
\ No newline at end of file
diff --git a/packages/http-client-python/generator/pygen/codegen/serializers/parameter_serializer.py b/packages/http-client-python/generator/pygen/codegen/serializers/parameter_serializer.py
index 6607fe02bd6..9091f86748d 100644
--- a/packages/http-client-python/generator/pygen/codegen/serializers/parameter_serializer.py
+++ b/packages/http-client-python/generator/pygen/codegen/serializers/parameter_serializer.py
@@ -202,9 +202,11 @@ def append_pop_kwarg(key: str, pop_type: PopKwargType) -> None:
                 if is_content_type_optional and not type_annotation.startswith("Optional[")
                 else type_annotation
             )
-            if kwarg.client_default_value is not None or kwarg.optional:
+            if kwarg.client_default_value is not None or kwarg.optional or kwarg.constant:
                 if check_client_input and kwarg.check_client_input:
                     default_value = f"self._config.{kwarg.client_name}"
+                elif kwarg.constant:
+                    default_value = kwarg.type.get_declaration(None)
                 else:
                     default_value = kwarg.client_default_value_declaration
                 if check_kwarg_dict and (kwarg.location in [ParameterLocation.HEADER, ParameterLocation.QUERY]):
diff --git a/packages/http-client-python/generator/test/generic_mock_api_tests/test_typetest_scalar.py b/packages/http-client-python/generator/test/generic_mock_api_tests/test_typetest_scalar.py
index 32a1583ac11..215018d1b83 100644
--- a/packages/http-client-python/generator/test/generic_mock_api_tests/test_typetest_scalar.py
+++ b/packages/http-client-python/generator/test/generic_mock_api_tests/test_typetest_scalar.py
@@ -51,3 +51,8 @@ def test_decimal128_verify(client: ScalarClient):
 def test_decimal_verify(client: ScalarClient):
     prepare = client.decimal_verify.prepare_verify()
     client.decimal_verify.verify(reduce(lambda x, y: x + y, prepare))
+
+
+# open this test case after adopt new version of http-specs for https://github.com/microsoft/typespec/pull/8807
+# def test_constant_query(client: ScalarClient):
+#     client.constant_query.post()