Aiming at the problem that the traditional soft threshold and hard threshold denoising methods can’t effectively solve the problem of noise interference in harmonic detection of power system, a new denoising algorithm is proposed： the improved soft and hard threshold tradeoff method. Use Matlab to simulate the signal of power system adopt the traditional hard、 soft threshold method, soft and hard threshold tradeoff method and the method in this pape. The quantitative comparative analysis shows that: the improved soft and hard threshold tradeoff method can restrain noise pollution better, improve the signal-to-noise ratio of the denoising signal, reduce the RMS error, the reconstructed signal can better restore the original signal , obtains a good denoising effect and have high practical value.