The damage model and the rate equation of quartz glass were set up under charged particles irradiation, and the concentration of ions and electrons produced by ionization were also given. The mathematical fitted results of the change in optical density are in accordance with the experimental results. The model was also applied to optical Al film reflector, and the mathematical fitted results of the integral reflectance of Al film reflector were given. The proposed damage model can be used to describe quantitatively the change in optical property of quartz glass with increasing absorption dose under charged particles irradiation.