Abstract: In order to solve the serious problem of energy loss in long distance diffuse reflection laser ranging system and improve the response speed of ranging system, a receiving lens with small detecting target surface and large clear aperture was designed. The three groups of 4-slices Petzval mode were used as the initial prototype of receiving lens, the aperture diaphragm was placed forward in the first side and its aperture was increased to improve the receiving efficiency. The concave of the last lens was designed as aspheric shape, which aimed to reduce the spherical aberration and miniaturize the system, and an avalanche photodiode detector with the diameter of 75 µm was used for the target surface to ensure the response speed was less than 45 ns. The receiving lens with the clear aperture of 120 mm is obtained by the optimized design, and its F-number is 0.6, which can be used in the field of long distance diffuse reflection laser ranging.