Based on energy deposition theory of Sigmund, the model of thickness of energy perturbation layer caused by low energy ion bombarding optical surface is built up. Beam current density on the optical surface is obtained by theory analysis, and the model of thermal deposition caused by low energy ion bombarding optical surface is built up. TRIM program is used to simulate the collision between low energy ions and atoms on the optical surface. And then, contributions to the thermal deposition and energy perturbation layer thickness from parameters such as ion energy, ion type and incidence angle are discussed. Finally, by taking the thermal quantity of deposited workpiece as a heat source in ANSYS, temperature field, thermal gradient field and stress field of the workpiece are obtained. The temperature and thermal gradient of the surface radiated by ion beam each present a Gaussian profile, and decrease along the radius from the center to the edge. The stress on the surface is a compressive stress within the radius of Half Maxim, and it is a tension-tension stress from the radius of Half Maxim to the edge.