In order to improve the accuracy of harmonic detection, reduce harmonic leakage and fence effect. In this paper, the improved windowed interpolation FFT and HWT algorithm are used to detect the non integral harmonics. And using STM32 + DSP Dual CPU parallel processing technology to complete harmonic detection, and through MATLAB simulation and experimental analysis, it can be concluded that through the introduction of windowed interpolation FFT algorithm and harmonic wavelet method, non integer harmonics can be effectively measured, and achieve the desired effect, with a certain practical significance.