The optical method of differential laser Doppler for the ship wake detection was studied. The characteristics of the backscattering light for the bubble and turbulence were experimentally studied. The velocity of the ship wake field was obtained by the laser differential Doppler method, which is in coincidence with the actual value, and the relative error is less than 1.5%. The experimental results show that the angle between two coherent beams has obvious effects on the frequency shift. And the frequency shift increases as the angle increases. The frequency shift spectra for the bubble are characterized by a universal profile and at the low frequency end. The full width at half peak of the profile becomes larger as the field intensity increases, which can be seen as a criterion of the wake recognition.