回复：出境时I94卡忘了交回，是否需要寄回给移民局？

还保存着前几天离开美国的航班地登机牌，

这是否可以成为离境依据？

-Yes.

下次入境时万一碰到问题，出示离境的登机牌是否足够？

--Plus 你的护照进入中国入境验讫章 and 出中国出境验讫章. 

 

如果需要寄回I 94卡，请问寄送的地址是哪里？

-If you will return to US shortly (e.g. a couple of months), you may not need to send the I-94 to the CBP office, but if you will stay in China for a longer time (e.g. > 4 months), you had better send the I-94 and the above evidences of your travel to the following address (keep the copy of these evidences on your file):

DHS - CBP SBU

1084 South Laurel Road

London, KY 40744

USA

Read this website for more details:

https://help.cbp.gov/app/answers/detail/a_id/752

谢谢。