Abstract: In order to realize the automatic focus of laser projection system, a laser dynamic focusing system was constructed. The system can adjust the mirror group spacing of the focusing system according to the change of the back-reflected light intensity signal, so that the laser scanning projection system can focus the minimum spot on the projection surface at different distances, thereby improving the positioning accuracy of the system. Firstly, according to the principle of laser dynamic self-focusing system, two kinds of dynamic self-focusing schemes, optical lever type and inverted telephoto type, were designed and the corresponding mathematical models were derived; then, through the simulation of ZEMAX, two dynamic focusing systems were compared, and the self-focusing system with faster response speed and more reasonable structure was chosen; finally, a new self-focusing laser scanning projection system was set up, and the performance of dynamic focusing was verified. The experimental results show that the inverted telephoto type self-focusing system is more reasonable, at a projection surface of 4.5 m, the converging spot diameter is optimally up to 0.2 mm, which can improve the positioning accuracy of the laser scanning projector during auxiliary assembly to 0.1 mm. It can meet the precise positioning requirements of components in advanced manufacturing and assembly engineering.