Aimed at multi-frequency signal, based on the analysis of spectral leakage feather of rectangular window, extremeum method is used to search the needed spectra to be corrected, and then the corrected frequencies, amplitudes and phases are calculated using energy centrobaric method. The method has low computational complexity, which can find the spectra to be corrected rapidly and correct them, and can meet the need of real-time monitoring in engineering. The results benefit the applying of correction technique of discrete spectrum in engineering.