Abstract: In order to extract partial discharge signals from the strong noise interference generated in the process of on-line partial discharge monitoring,the method of combining wavelet packet transform and mathematical morphological filter is used to denoise the partial discharge signal containing noise. Wavelet threshold method,EMD method and the proposed method are used to denoise the partial discharge signal after mixing various noises. The simulation results show that the denoised waveform of the proposed method is the closest to the original waveform,the waveform distortion rate is the lowest,and has a good denoising effect.