-If he filed O-1 application before H-1 expired, he was legally present during the O-1 pending. So, as long as he will go to China very soon, he should be fine to get the visa. Bring the last H-1 approval notice and the O-1 denial notice to prove his legal stay during the O-1 pending during the visa interview.
簽過了的話入關有問題嗎? 如果有可能,是簽h4 還是j1 好?
-H-4 visa is easier to get than J-1 visa (he can change H-4 to J-1 within US later).