Abstract: This paper deals with the spectrum autocorrelation method.A certain time window with a fixed width is set and moved along the time axis of a signal.The sections of the signal observed from the time window are transformed into the frequency domain using Fourier transform,and the correlation between them is then calculated.The noises of a room air conditioner and a running ship are analyzed using spectrum autocorrelation.The periods of their spectrum autocorrelation are respectively consistant with the vibration period of the refrigeration compressor and the rotating period of the axle of the propeller.