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我在A公司之前工作的公司的有一个approved的H1-B还没有过期，那么B公司的H1-B petition是否可以建立在最先的公司的H1-B的基础上？
-No, but if you do that, your H-1 status will have a gap and thus, the H-1 transfer petition by B Company probably still will be approved, but the approval may have no I-94. Thus, you need to go to China to get the H-1b visa to come back to activate the H-1b status to work for B Company.

So, you have two choices: 1. Ask A Company to use premium processing to get the H-1 petition approved, then do H-1b transfer to B Company as the B Company lawyer suggested; 2. do H-1B transfer from the old company to B Company as you mentioned here, and then go to China to get the H-1b visa..

 谢谢！