In order to realize low Doppler detection of high-speed moving targets,a difference frequency detection method of dual frequency coherent laser is proposed. The optical factors affecting the difference frequency signal generated by the dual-frequency laser coherence are analyzed. Firstly,the power spectrum function of the differential frequency light is derived by using the Wiener-Khinchin theorem. Then,the frequency domain integral method is used to get the difference frequency optical signal to noise ratio,and the fringe contrast of the difference frequency optical signal is analyzed. Finally,the experimental study on the difference frequency signal generated by dual frequency laser coherent mixing is carried out. Theoretical analysis and experiments show that the increase of laser line width leads to the decrease of difference frequency optical signal-to-noise ratio and fringe contrast,and the smaller the difference of optical path,the better the fringe contrast,and the frequency disturbance of frequency shifter leads to the fluctuation of difference frequency optical center frequency.