This invention discloses a P-RACH open-loop power control method in the TDD system including: a base station gets the expected receiving power of the UpPCH from a radio network controller to test its actual receiving power of user terminal UpPCH, compensating the P-RACH expected receiving power of said user terminal based on the difference of the expeted and actual receiving power. This inventionalso discloses a base station using said method and can modify the user terminals with open power control at the positive deviation and negative deviation suitably.