On the basis of the analysis of the Rife-Vincent window and the characteristics of triple-spectral-line interpolation algorithm, an approach for power harmonic analysis based on the Rife-Vincent window and the triple-spectral-line interpolation is proposed to solve the problems of fast Fourier transform in the power harmonic analysis, the modified formula is obtained by using polynomial fitting method and simulation of the power harmonics is made based on it. The simulation results show that under the same condition, it takes less than 0.225 ms and the amplitude correction error is less than -1.4×10-6 % with the simple harmonic signals processed, while it takes less than 0.997 ms and the amplitude correction error is less than -9.68×10-6 % with the complex signals dealt with. Therefore, the algorithm has not only higher detection precision, but also faster operation speed.