回复：请问8老师

我离开美国快四年，绿卡是不是自动失效，要不要上交。谢谢。
-Yes, your green card is void. But you still had better abandon the green card in a US Consulate outside US (e.g. in China) in case US Government ask you to pay income tax, etc.
See the following website about green card abandonment:
http://shanghai.usembassy-china.org.cn/green_cards_holders.html
http://www.immihelp.com/greencard/abandonment-greencard.html