The method of combining numerical simulation and experiment is adopted for the optical system of a high power direct writing device,and the heat dissipation structure of a lens barrel is designed. The thermal analysis and stress strain analysis of the structure of the optical system were carried out by finite element analysis software,and the analysis results showed that the laser power of the optical system was 100 W,and the highest surface temperature of the lens barrel made of SUS304 and AL6061 was concentrated in the area near the prism box,with a maximum temperature of 59.016℃,and the overall temperature uniformity and heat dissipation performance were poor. The test results show that when the heat dissipation system is working normally,the overall temperature difference of the system is only 0.99℃,which meets the requirements of temperature uniformity,and the DMD calibration error is less than 15μmand the center position drifts in the same direction,which meets the technical index requirements of less than 20μm,which is conducive to the image stitching when the system is exposed,and verifies the effectiveness of the heat dissipation design.