Abstract: With the terminal on satellite in the orbital motion thermal condition, optical antenna mirror surface thermal distortion will badly affect the performance of laser communications links. Applying finite element method to analyze shows that normal angle deviation of mirror body before and after thermal tension being released can be nearly 3 order magnitude which is 10-7 radian when reasonable application of pressing-plate method. Pressing-plate method is, in certain condition, a more optimum solution of fixing method to the working way of terminal on satellite in space-to-ground laser communication links.