Abstract: In order to improve the detection sensitivity of a spaceborne lidar, high gain amplifier circuit was used to design the detection circuit. The relationships among detection probability, false alarm rate, signal-to-noise ratio and other indicators were analyzed theoretically. Bandwidth, gain, threshold and other parameters were optimized. Experimental verification was also carried out. The results show that the sensitivity of detection circuit is 9nW, the detection probability is 95%, and the false alarm probability is 10^-5. Compared with the domestic similar products, the detection circuit has been significantly improved. The study is helpful for the development of spaceborne lidars.