Why in unity editor l can get steam achievements, but without the editor l can't? !

It probably has to do with your init of steam. Maybe because it uses the txt file steam_appid.txt in the editor...

This is my code (Insert your app_id). Hope it helps.

 bool InitValve()
 {
     try
     {
         if (SteamAPI.RestartAppIfNecessary((AppId_t)app_id))
         {
             Debug.LogError("[Steamworks.NET] SteamAPI.RestartAppIfNecessary returned false\n", this);
             return false;
         }
     }
     catch (System.DllNotFoundException e)
     {
         Debug.LogError("[Steamworks.NET] Could not load [lib]steam_api.dll/so/dylib. It's likely not in the correct location.\n" + e, this);
         return false;
     }

     bool bSteamAPIInited = SteamAPI.Init();
     if (!bSteamAPIInited)
     {
         Debug.LogError("[Steamworks.NET] SteamAPI_Init() failed.", this);
         return false;
     }

     // cache the GameID for use in the callbacks
     gameID = new CGameID(SteamUtils.GetAppID());
     UserStatsReceived = Callback<UserStatsReceived_t>.Create(OnUserStatsReceived);
     UserStatsStored = Callback<UserStatsStored_t>.Create(OnUserStatsStored);
     UserAchievementStored = Callback<UserAchievementStored_t>.Create(OnAchievementStored);
     bool bSuccess = SteamUserStats.RequestCurrentStats();

     // get user name
     iUserID = SteamUser.GetSteamID().m_SteamID;
     szUser = SteamFriends.GetPersonaName();
     bUserValid = true;

     return true;
 }