when I re-entered US, the stamp on my I94 shows "Paroled/ AOS" , does that mean I am currently
on the status of AOS and no more H1?
-Your current status is AOS, but you still can re-instate your H status by going outside US to get an H1 visa, doing h1 extension or doing H1 transfer without affecting your I-485 (using AP is different from using EAD).
but I have not applied EAD yet and still use H1B currently. Another fact is, I am going to quit the job here and go back to China to stay there for about half a year, and once I quit the job, my H1B will be invalid and I apply the AP/EAD before I leave for China. In that case, a school or company in US (if any) can still apply a H1B for me to return to US to work (If I don't want to use EAD or if I stay in China over a year and my AP becomes invalid)?
-Yes. But if you receive RFE for your emploment status for your I-485 and you is not in US or you have no job in US, USCIS will deny your I-485. Your overstay outside US (> one year) will affect your I-485.
Anyway, you can come back to US anytime in the future using H1 visa.