Abstract: In the low Earth orbit, the low-energy proton irradiation is an important factors for the damage of the space optical elements. The laser highly reflective film is an important part of the space laser system for the laser generation and output. Its performance directly affects the stability of the laser system. In this paper, the ground space environmental simulation device is used to simulate the effect of the proton (40 keV) acted below. The surface morphology and the photothermal absorption characteristics are obtained by the fixed-point in-situ measurement and the photothermal absorption test. The laser damage threshold measurement is made to characterize the laser damage threshold and the damage morphology of small initial damages. The specific process of the particle transport in the material is simulated by using the SRIM program, and the energy loss in the process is quantitatively analyzed the experimental results show that the 40 keV proton irradiation eventually has a significant effect on the laser damage properties of the HfO₂/SiO₂ three-band high reflectivity films.