回複：謝謝你，863211，還想跟你確認一下

我google了一下，這個I-90form看起來是給那些已有綠卡但可以丟失或沒收到用的，填了這表，交$290,加上一些需要的證明材料，就可以補辦。所以我想是不是一入美國海關時，就要告訴移民局將要居住的地址什麽的和其他信息，然後移民局在一定時間內就自己給你寄來綠卡卡片，也就是不用申請---純屬我自己的想象哦。
-You are right. When you enter into USA with your immigrant visa, passport, the documents given by the consulate sealed envelope given by the consulate. At the port of entry, after your basic interview you may be taken to the immigration office at POE where immigration officer will review the document and issue a I551 stamp ( temporary green card stamp) this stamp is valid for one year. You will receive an actual plastic green card via regular mail within few months.

第二個問題是回美證，應該是大於6個月但小於1年的話，到當地辦公室在綠卡上蓋個章就行；
-The green card stamp in the passport is valid only for one year, he can go to China and come back before the stamp expires if he has no the physical green card yet.
如果離開美國超過了1年，在這個情況下就要申請回美證。我的理解對嗎？
-Yes, if he plan to stay outside US >one year -