Abstract: In view of the poor analytical accuracy and weak real-time performance caused by signal noise and harmonic wave exist in the voltage sag detection, a comprehensive voltage sag detection method is proposed to weaken the impact of the interference signals by the double wavelet analysis. This method decomposes the signal at multi-scale with db20 wavelet to catch the fundamental wave, and then decomposes the fundamental wave at single-scale with db10 wavelet to detect the modulus maximum of high-frequency components. The proposed method can suppress the interference signal and improve the performance of voltage sag detection by wavelet analysis.