The performance of laser detection system (LDS) is directly influenced by the velocity identification capability. Due to the bandwidth restriction of the receiver, the laser Doppler shift of the high speed targets can not be detected in LDS. A dual-frequency laser coherent detection (DLCD) system is introduced consequently, which has successfully solved the problem and enhanced the system capabilities obviously. Based on the theory of the DLCD, the signal-noise ratio (SNR) influenced by the amplitude disturbance, the phase disturbance and the frequency disturbance are analyzed, and the characteristics different from the signal-frequency laser coherent detection (SLCD) are illuminated. The simulation results indicate that the amplitude disturbance effect on the SNR of DLCD is consistent with that of the SLCD. For various kinds of frequency and phase disturbance, the SNR of DLCD is higher than that of the SLCD. When the phase disturbance increases to 0.5π, the SNR of SLCD is 0 dB, while the DLCD is still higher than 18 dB.