This article, which is based on the topology optimization theory, considered the lightweight design of large aperture reflectors. Firstly, the material selection is based on the low temperature environment and the low temperature infrared optical mechanical structure design principles. Then, by using the minimum deformation of the mirror surface as the objective function, mirror volume and rigid body displacement as design restraints, and imposing manufacturing constraints, a conceptual design of the mirror back with manufacturability was accomplished. Finally, by using the finite element analysis method to compare the performance of the topologically optimized mirror and the primal mirror, it shows that the topologically optimized mirror met the design requirements in terms of lightening effect and structural rigidity, and the surface figure met the requirements under the influence of gravity, which emphasizes the feasibility and practicality of topology optimization in the large aperture mirror' design. © 2020 SPIE. All rights reserved.