In this paper, we propose an effective method to compensate the performance degradation of optically addressed spatial light modulators (OASLM). The thermal deposition problem usually leads to the reduction of the on-off ratio of amplitude OASLM, so it is difficult to achieve better results in high-power laser systems. Through the analysis of the laser-induced temperature rise model and the liquid crystal layer voltage model, it is found that reducing the driving voltage of liquid crystal light valve and increasing the driving current of optical writing module can compensate for the decrease of on-of ratio caused by temperature rise. This is the result of effectively utilizing the photoconductive effect of Bi12SiO20 (BSO) crystal. The experimental results verify the feasibility of the proposed method and increase the laser withstand power of amplitude-only OASLM by about 2.5 times.