Space-based two-dimensional turntable is the main load-bearing structure of space photoelectric detection equipment, and the collimation frame is the key support component of turntable, so its stiffness characteristics are vital for the performance of turntable. In order to decrease the mass and improve the stiffness performance, the structure of collimation frame was topologically optimized based on the variable density theory by finite element software -MSC. Patran/Nastran. Modal shape of collimation frame was regarded as the deformation of model under the thrust. The model was optimized with stiffness maximization as the objective function, the ratio of residual volume as the constraints. The results show that the model weight after optimization is lighten 1.32 kg and the first-order natural frequency increases 14.5 Hz compared with the model of experience design. The maximum deformation is relatively reduced by 22.4% and the maximum stress value is relatively reduced by 42.6% under the action of gravity in the Z direction and the statics characteristic of model are increased significantly in the other directions. The dynamic characteristics of the collimation frame are improved significantly with the weight reduction. Modal experiment was done for the optimization model and the results indicate that the finite element analysis is correct. Therefore, it is feasible to use the method of topology optimization to design the structure of collimation frame. © 2017, Editorial Board of Journal of Infrared and Laser Engineering. All right reserved.