回複：86等高手,請幫忙關於回國後綠卡是否能保住的問題??很很感謝!

You can not stay in China continuously for more than 6 months, otherwise your physical presence continuity for the US citizenship will be disrupted. As for whether your green card will be affected or not, here is an artilce for your reference:

http://immigration.wenxuecity.com/BBSView.php?SubID=cdh&MsgID=628