when you say you have "回美證", do you mean it is Advance Parole? AP is only good for one year. If you enter the US after its expiration, you will be rejected an entry. So first thing, be sure that you return the US before your AP expires. When you are in the US you should apply for renewal of your AP before you leave again. You cannot apply AP when you are outside US but you can wait for the approval in China.
If your I-485 is approved when you are in China, You still need to use your AP to enter. Then make an appointment throug INFOPASS to go to your local CIS to get an I-551 stamp on your passport. Some local CIS have changed the procedure. CIS will request you to have biometrics taken first then approve your GC. In this case, you will receive the green card itself through mail, no more I-551 stamp on the passport.
In any case if you receive your I-485 approved while you are in China, you still need to use your AP to enter the US. So your AP is very important document for travel purpose.
If your I-485 is approved when you are in China, You still need to use your AP to enter. Then make an appointment throug INFOPASS to go to your local CIS to get an I-551 stamp on your passport. Some local CIS have changed the procedure. CIS will request you to have biometrics taken first then approve your GC. In this case, you will receive the green card itself through mail, no more I-551 stamp on the passport.
In any case if you receive your I-485 approved while you are in China, you still need to use your AP to enter the US. So your AP is very important document for travel purpose.
