Abstract: Speech enhancement algorithms based on short-time Fourier transform with the advantages of good effect and low calculation complexity, is widely used. The main parameter of this kind of algorithms is the power spectrum, which is the power of amplitude spectrum. In this paper, an ideal for cutting amplitude spectrum to correct power spectrum is presented, which is supposed to improve the relative signal-to-noise ratio between voice existence and voice inexistence, and finally to restore the low SNR speech. Speech enhancement algorithms based on short-time Fourier transform would get a better result by introducing cutting algorithm to correct power spectrum. The ideal is to subtract a small value from the amplitude spectrum which below the threshold value, and to recalculate the power spectrum using the cut amplitude spectrum. Then the relative SNR between the high power position and the low power position could be improved. For the high power position usually stays for the speech existence, then the speech existence could be distinguished more easily from the speech inexistence. This benefits the following speech enhancement. The experiment results is given at the last of the paper. The spectrogram and PESQ test show the presented algorithm worked.