In the laser communication system, the detection accuracy of the laser light spot is of great significance to the communication system. In order to improve the accuracy of light spot positioning, a laser nutation positioning algorithm based on photodetector is proposed, the basic principle of space light to single mode fiber coupling is analyzed, and the effect of lateral offset on coupling efficiency is studied, and the expression of the nutation positioning algorithm is derived. In this paper, the positioning accuracy of nutation algorithm and the parameters affecting nutation scanning are analyzed by Matlab simulation. The simulation results show that the positioning accuracy of the nutation positioning algorithm is 0.04 μm, which meets the requirements of the communication system for light spot detection.