The topological optimization design of a primary mirror is carried out to resolve the contradiction between the excessive change in the surface figures and the light weight of the primary mirror under high rotation speed. The primary mirror is divided into hexahedral elements by HyperMesh software, and the displacement of all nodes on the two surfaces of the primary mirror along the central axis of the primary mirror is defined as the response. The root-mean-square (RMS) error of surface figures (relative to static surface figures) is used to evaluate the surface figure change of the primary error and is taken as the optimization constraint, and then the topological optimization of the primary mirror is performed with the goal of the lightest weight. The optimized structure is reconstructed geometrically and substituted into OptiStruct for recalculation; the primary mirror is processed according to the reconstructed model, and the RMS error of surface figures after optical fabrication is measured by an interferometer. The optimization results indicate that the RMS error of the surface figures is below 0.35 μm, and the weight is reduced by 38.54%. The surface figure accuracy of single-point turning is 0.08 μm (obtained by calibration), and thus the RMS error of surface figures after optical fabrication does not exceed (0.35+0.08) μm in theory. The surface figures of mirror 1 and mirror 2 measured by the interferometer after light addition have an error of 0.36 μm and 0.31 μm separately relative to the theoretical surface figures of the single-point turning, which are all less than 0.5 μm.