A kind of resonance frequency detection of piezoelectric micro-cantilever is presented, where there is piezoelectric film deposited. The alternating current is put on the film to make it vibrate, and when resonance frequency happens, the amplitude of piezoelectric micro-cantilever reaches the maximal. A series of experiments have been done by the driving power and detecting power designed by ourselves. The experiments show that resonance frequency can be detected by the amplifier, and the amplitude of the resonance frequency is obviously bigger than the amplitude of the other frequency. The maximal amplitude is about 600nm.