Abstract: Due to the wide use of non-linear components, harmonic problem becomes increasingly serious. Fast Fourier Transform (FFT) has been widely used in the analysis of power system harmonics. But the results will be disturbed by the spectrum leakage. Some efforts have been made including the utilization of window functions and interpolation algorithms to correct the measured frequency, phase and amplitude by FFT. In order to overcome some shortcomings of existing correction methods, This paper proposed a method combines FFT with the Multiple Modulation Zoom Analysis based on Complex Analytic Band Pass Filter (Improved ZFFT ) and then have verified the effectiveness and practicability of the algorithm.