I would like to ask if i have a transimitter,how can i check its baud rate?
Do you mean in your embedded software, or do you want to measure it manually? To do it in software, search for "auto-baud" To measure it, use a scope. If you think it's a standard rate, trial & error with a terminal!
Google is your friend: http://www.google.com/search?hl=en&lr=&ie=UTF-8&q=baud+rate+auto+detection&btnG=Search