To increase the laser damage threshold, an ion-beam assisted electron-beam formation method is used for preparing high-reflection films with three wavelengths of 355, 532, and 1064 nm. First, Lambda 950 spectrophotometer is used to test the spectral performance of the film sample. Then, the influence of different substrate materials and substrate cleaning processes on the laser damage threshold of the film are verified. Finally, the weak absorption capacity of the film and the laser damage threshold under different working vacuum degrees are studied systematically, and the relationship between the weak absorption capacity of the film and the laser damage threshold is analyzed. Additionally, the relationship between the weak absorption of the thin film and the laser damage threshold value is analyzed. The results show that the reflectance at the three wavelengths meets the requirement of optical performance indicators for the solid-state 355-nm ultraviolet laser. The laser damage threshold of the film and weak absorption value do not correspond to each other when the working vacuum increases to a certain level. However, an optimal value indicates that the high-reflection film can be used as the mirror in an all-solid-state 355-nm laser.