The fast Fourier transform(FFT) will have a greater error in the cases of non-synchronous sampling and in a truncated non-integral period,thus accurate harmonic parameter values can not be obtained.Widely used for harmonic analysis in the electric power system,the windowed interpolation fast Fourier transform(FFT) algorithms could compensate the spectral leakage in frequency domain caused by non-coherent sampling and non-integral period truncation,and subsequently the accuracy of harmonic parameters measurement couldbe improved.The spectral characteristics of Blackman-Harris window were analyzed and an approach for harmonic analysis based on Blackman-Harris window interpolation FFT was proposed.The applicable rectification formulas of the interpolation were obtained by using polynomial curve fit functions.The simulation results indicate that the approach based on Blackman-Harris window interpolation FFT can be designed and realized easily and restrain spectral leakage effectively.