Finally I found how to use bulit-in timer in Flash.
(Before I know it I always used X keyframes to mean 1 second)
And this small program let you check the movie's FPS at any time,when the clip exists in the movie.
Try put it at a complex movie,and......HEHEHE
File Format :
Flash MX (or higher)
How to use :
Just drag "Easy FPS System" movie clip into your movie,very simple.