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我在F1期间曾出境半年，这个会ERASE之前的J1吗？

-What do you mean "Erase the J-1"? After you changed your status to F-1, then you lost your J-1 status (you only can have one type of status at one time) unless you reenterd US using J-1 visa after you left US.  Based on the immigration law, because you got J-1 waiver, you can not get the J-1 visa outrside US or change your status to J-1 within US anymore.