In order to reduce the medium and low frequency noise of mine axial flow fan, a kind of local resonance phononic crystal double-layer plate was designed, and a sound insulation performance evaluation method was proposed. Based on the evaluation method, the structure parameters of the phononic crystal double-layer plate were optimized by COMSOL Multiphysics software. The results show that the band gap width of phonon crystal veneer decreases with the increase of coating thickness, but increases with the increase of oscillator radius. In the specific frequency band, the sound insulation performance of the designed phononic crystal double layer plate is better than that of the phononic crystal single plate. The sound transmission loss of the phononic crystal double-layer board is 10 dB higher than that of the phononic crystal board in the target noise reduction frequency band (200 Hz~800 Hz) of the axial flow fan, and the STL at the peak noise frequency (500 Hz) reaches the maximum value of 58 dB, and there is no obvious low frequency band of sound insulation, which has a good sound insulation effect.