A kind of improved M-Rife algorithm is introduced in this paper for the accurate analysis of harmonics in the power system. This method overcomes the problem of spectrum leakage and fence effect due to asynchronous sampling in normally used Fourier analysis. This method makes the asynchronous sampling issues be synchronized by moving the frequency spectrum. The advantage of the algorithm is the application of M-Rife idea to the harmonic analysis

and the big error due to the nonlinearity during interpolation process is overcome. It is verified by the test that the algorithm has higher accuracy and can analyze each parameter of harmonic effectively under the noise.