S-transform is an important tool in the analysis of power quality disturbances. In order to detect the power quality disturbances accurately, a method based on amplitude summation and the average of amplitude quadratic sun of S-transform module matrix are proposed. The summation algorithm gets the envelope of amplitude of time and frequency. The average of amplitude quadratic sun algorithm can locate the time of disturbances and detect the frequencies. Compared the power quality disturbances analysis of S and Daubechies wavelet and wavelet packet transform by Matlab stimulation, the result proves that S-transform is more accurate.