回复：请问法居士或其他知道这方面情况的--绿卡持有者可以离境多久？

Legally you can reenter the US with your greencard within one year. If you want to leave US for more than one year, you have to get AP. However, in some cases the custom USCIS officer will ask you why you leave US for so long since the reason for you to get greencard is that you want stay in US premanently. If you don't have any reasonable answers, they may take your greencard at their discretion, then you have to go to court to take it back.