LiDAR, as a kind of sounding and underwater terrain drawing equipment, has entered the commercial use stage abroad. In China, the development and application of LiDAR are relatively slow, and researchers mainly focused on the development of large-scale dual-frequency water measurement LiDAR. Based on the design of dual-frequency water measurement LiDAR, a single-frequency LiDAR opto-mechanical system for Unmanned Aerial Vehicle(UAV) was designed by author's team. Firstly, the system component was designed separately. Namely, a reflective optical wedge was used by a scanning unit to achieve transmission scanning, an optimal receiving angle of view was calculated by the Kopilevich model, and a receiver optical unit was designed with generalized Kepler system. Then, the whole machine was integrated, the efficiency of the optical system was calculated, and a simulation experiment was used to verify the scanning effect, a waveform test was used to verify the usability of the designed LiDAR. The characters of this system are as follows: the optimal receiving view angle is 95 mrad, the best flight altitude is 150 m, flying speed is 10 m/s, the best depth of measured water within 25 m, the maximum depth of measured water is 50 m. The Kopilevich model is used to determine the best LiDAR field of view to improve the performance of the LiDAR opto-mechanical system, two different scanning methods can be switched.