Abstract: In order to solve the problem of white noise and periodic narrow-band interference in the field detection of partial discharge in cable terminals, a noise reduction method based on generalized S transform and singular value decomposition is proposed. In this method, the number of narrowband interference is obtained by the generalized S-transformation adaptively and the segment where the partial discharge is intercepted. Then the improved 3 spectral line interpolation method is proposed to accurately estimate the narrowband interference frequency and construct the guide signal to be added to the original signal. This signal is decomposed by the singular value to suppress the mixed noise. The method in this paper is used to the simulated and measured partial discharge signals, and compared with the traditional denoising method. The results show that this method has better suppression effect on mixed noise interference and can restore PD signal well.