Thank to Maomao2003 and Rosewhite for answering my question. I still have another question. Originally one has H1 visa and he needs to change it into H4. Suppose he has filed the appication for H4, and quit the job before receiving the H4 visa, will he still be able to stay in the U.S. legally and how long he can stay? Thank you very much in advance for your reply.