when measuring the frequency of the control module's power and the feedback signal, traditional measuring methods susceptible to noise, temperature and circuit parameters. It is difficult to achieve the required accuracy for these methods. In this paper, a discrete Fourier transform and interpolation analysis method will be used, using the fast Fourier transform to analysis signal's spectrum first. Then It discusses the causes of error and method for reducing errors and improving accuracy by interpolation method. Finally, the experiments showed that the measurement results within the accuracy requirements. The method can meet the requirements of using.