自己解决了
SS6.4的参见
http://www.twcenter.net/forums/showthread.php?659966-New-Steam-Update-quot-fix-for-mods-quot

原来官论上有解决方法，真简单
Hi guys,
this is what I tried for Stainless Steel 6.3/6.4 to make it work with my Steam M2TW game and it worked...!!!!!!
So, STEAM Users, follow these steps...!
1. Put @mods\SS6.3\default.cfg phrase in SET LAUNCH OPTIONS of the game in Steam (Select the game in your Steam Library, right click it and select Properties).
2. Go to the installation directory (usually C:\Program Files (x86)\Steam\SteamApps\common\Medieval II Total War\mods\SS6.3) and find the file called default.cfg (the one that you just put into launch options to start with). Open it with a text editor (e.g. Notepad).
DO NOT FORGET TO make a reserve copy of this file before you change it!
3. Change the phrase "kingdomDir=" into "medieval2Dir=" then save and close the file.
4. Launch the game from Steam as usual.
Enjoy your hack now...!