After 70,000 miles i replaced all belts including the timing belt,the belt squeal went away after 1 day of driving it's back again.how do i find out which belt and the root cause?

 

It's probably a loose belt. Check for deflection. If you press on the long run with you finger, can you get it to bend 5mm? If it's much looser, then that's the problem.

Another way to pinpoint the problem is get a rubber hose and stick it in your ear. With the other end, search for the source of the noise.