From south Asian coming to America for study, and this year I'm going to graduate from high school. I'm not international student But I'm Permanent Residence of Us. I had a 10 years Legal and have a full right to fly back to country and also living here in America. My question is I want to be a flight attendant after high school, but not really sure yet because I'm not a US citizenship yet so it's possible to be as a flight attendant ? What is the flight attendant requirement ?

Not a problem, as long as you maintain 50% of the year in US your resident status is safe.

As a legal resident you can and of course always go back to your own nation and become one also. There are attendants in all nations.