Abstract: In order to solve problems of frequency spectrum leakage and picket fence effect in harmonic detection by Fourier transform, the paper proposed a harmonic detection method, which uses 2-order Haining convolution window to reduce frequency spectrum leakage and interpolated correcting algorithm with double-peak of spectrum lines to restrain picket fence effect. The Matlab simulation result showed that the harmonic detection method has high detecting precision for harmonic in steady state and improves frequency spectrum leakage and picket fence effect well. For fluctuation harmonic, it proposed a harmonic analyzing scheme integrated wave-let, Fourier transform, and windowing and interpolation algorithm.