In the progress of laser scanning projection calibration, the accuracy of the calibration is directly affected by the light spot size of the laser projection, and then affects the projection accuracy of the projection system. In order to meet the requirements of the laser projection scanning system for accuracy, a method of improving the accuracy of the laser scanning projection is proposed. That is, the method of combining the fixed magnification collimation beam expander lens group and the dynamic focusing lens group reduces the laser beam divergence angle and laser projection spot at the same time, and the projection system in the projection of the working distance has sufficient depth of focus. Which can obtain a larger laser energy density, and then achieve the field of focus. The theoretical results are simulated and verified by using the ZEMAX optical design software through the experiment. In 4-5 m working distance, after the laser beam passes through a fixed radio collimating beam expander and the dynamic focusing lens group, it effectively reduces the laser beam divergence angle and projection light spot size, then improves the energy density of projection spot on the target locating point. Finally, the laser scanning projection system meets the requirements of the projection accuracy.