According to the statistical characteristics of signal and noise of diffuse-reflection target detection, analysis is made to the key parameters such as signal to noise ratio and receiving sensitivity of the coherent lidar.The research results show that:1) The receiving sensitivity is closely related to the requirement of false alarm rate and detection probability, as well as the dynamic range of target velocity and the detection wavelength;and 2) The sensitivity can be significantly improved by the mode of multiple detections.The research result is of great significance for the system design of coherent lidars.