Abstract: In order to achieve a proper structure and support for the primary mirror used in the space optic remote sensor and test the optical performance of a new optic material (SiC), 3D solid models were built for the primary mirror subassemblies. The mass and the center-of-mass of the primary mirror are analyzed for the different lightweight structures used on the backside of the mirror with the finite-element simulation method. Several finite-element models of the primary mirror were built with appropriate MPC boundary constraint. The effect of the mirror weight on its surface form accuracy during the fabrication and testing process is analyzed with finite-element method. The optimal structure for the mirror and its support were achieved through the comparison of simulation results and optimized lightweight design. The optimized weight reaches 75.6% of the original value, the RMS of the mirror surface is 12.53nm and the Pv value is 54.52nm. The result shows that the weight, stiffness and surface accuracy of the primary mirror meet the engineering requirement.