Comparing with the system which was designed for the ground application,the operation characteristics of space-borne laser remote sensing system are analyzed.According to the laser ranging equation,external factors which influence echo power are discussed.The design elements of echo detecting system are analyzed and the relation between detection probability and SNR is discussed.The optimal operation point setting technique and high bias voltage stability control technique of APD are studied in detail.Based on the theory of optimum liner filter designing,the theoretic design results,such as the bandwidth and gain of the receiver,are given in this paper.