diff --git a/apps/emqx_management/src/emqx_mgmt_api_app.erl b/apps/emqx_management/src/emqx_mgmt_api_app.erl
index 5649b1ca0..2da060b55 100644
--- a/apps/emqx_management/src/emqx_mgmt_api_app.erl
+++ b/apps/emqx_management/src/emqx_mgmt_api_app.erl
@@ -120,12 +120,12 @@ fields(app) ->
             )},
         {expired_at,
             hoconsc:mk(
-                hoconsc:union([undefined, emqx_datetime:epoch_second()]),
+                hoconsc:union([infinity, emqx_datetime:epoch_second()]),
                 #{
                     desc => "No longer valid datetime",
                     example => <<"2021-12-05T02:01:34.186Z">>,
                     required => false,
-                    default => undefined
+                    default => infinity
                 }
             )},
         {created_at,
@@ -219,7 +219,7 @@ api_key_by_name(put, #{bindings := #{name := Name}, body := Body}) ->
 format(App = #{expired_at := ExpiredAt0, created_at := CreateAt}) ->
     ExpiredAt =
         case ExpiredAt0 of
-            undefined -> <<"undefined">>;
+            infinity -> <<"infinity">>;
             _ -> list_to_binary(calendar:system_time_to_rfc3339(ExpiredAt0))
         end,
     App#{
@@ -228,4 +228,4 @@ format(App = #{expired_at := ExpiredAt0, created_at := CreateAt}) ->
     }.
 
 ensure_expired_at(#{<<"expired_at">> := ExpiredAt}) when is_integer(ExpiredAt) -> ExpiredAt;
-ensure_expired_at(_) -> undefined.
+ensure_expired_at(_) -> infinity.
diff --git a/apps/emqx_management/test/emqx_mgmt_api_app_SUITE.erl b/apps/emqx_management/test/emqx_mgmt_api_app_SUITE.erl
index 85f712fed..44fc09902 100644
--- a/apps/emqx_management/test/emqx_mgmt_api_app_SUITE.erl
+++ b/apps/emqx_management/test/emqx_mgmt_api_app_SUITE.erl
@@ -108,10 +108,10 @@ t_update(_Config) ->
     ),
     Unexpired1 = maps:without([expired_at], Change),
     {ok, Update2} = update_app(Name, Unexpired1),
-    ?assertEqual(<<"undefined">>, maps:get(<<"expired_at">>, Update2)),
-    Unexpired2 = Change#{expired_at => <<"undefined">>},
+    ?assertEqual(<<"infinity">>, maps:get(<<"expired_at">>, Update2)),
+    Unexpired2 = Change#{expired_at => <<"infinity">>},
     {ok, Update3} = update_app(Name, Unexpired2),
-    ?assertEqual(<<"undefined">>, maps:get(<<"expired_at">>, Update3)),
+    ?assertEqual(<<"infinity">>, maps:get(<<"expired_at">>, Update3)),
 
     ?assertEqual({error, {"HTTP/1.1", 404, "Not Found"}}, update_app(<<"Not-Exist">>, Change)),
     ok.
@@ -160,9 +160,9 @@ t_authorize(_Config) ->
     },
     ?assertMatch({ok, #{<<"api_key">> := _, <<"enable">> := true}}, update_app(Name, Expired)),
     ?assertEqual(Unauthorized, emqx_mgmt_api_test_util:request_api(get, BanPath, BasicHeader)),
-    UnExpired = #{expired_at => undefined},
+    UnExpired = #{expired_at => infinity},
     ?assertMatch(
-        {ok, #{<<"api_key">> := _, <<"expired_at">> := <<"undefined">>}},
+        {ok, #{<<"api_key">> := _, <<"expired_at">> := <<"infinity">>}},
         update_app(Name, UnExpired)
     ),
     {ok, _Status1} = emqx_mgmt_api_test_util:request_api(get, BanPath, BasicHeader),
@@ -172,9 +172,9 @@ t_create_unexpired_app(_Config) ->
     Name1 = <<"EMQX-UNEXPIRED-API-KEY-1">>,
     Name2 = <<"EMQX-UNEXPIRED-API-KEY-2">>,
     {ok, Create1} = create_unexpired_app(Name1, #{}),
-    ?assertMatch(#{<<"expired_at">> := <<"undefined">>}, Create1),
-    {ok, Create2} = create_unexpired_app(Name2, #{expired_at => <<"undefined">>}),
-    ?assertMatch(#{<<"expired_at">> := <<"undefined">>}, Create2),
+    ?assertMatch(#{<<"expired_at">> := <<"infinity">>}, Create1),
+    {ok, Create2} = create_unexpired_app(Name2, #{expired_at => <<"infinity">>}),
+    ?assertMatch(#{<<"expired_at">> := <<"infinity">>}, Create2),
     ok.
 
 list_app() ->