A method for ship wake detection is proposed, which is based on the characteristics of the laser Doppler shift spectrum of the backscattering light signal. A simulation of the Doppler shift spectrum because of the moving bubbles in wake is performed by Monte Carlo method. The influence of the bubble population and the velocity distribution on the laser Doppler shift spectrum is analyzed. Using the differential Doppler method, the influence of imitated wake on the Doppler shift spectrum is studied experimentally. Experimental results agree with the theoretical analysis basically. The results show that the amplitude and the cutoff frequency of the shift spectrum will increase with the increasing of bubble population and range of velocity distribution. It indicates the effectiveness of the detection method.