Abstract: Topology optimization design was conducted for an integrated aluminum alloy mirror with a diameter of 300 mm. Under the self-weight load along the optical axis of the mirror, the global flexibility was considered as a constraint, and the minimum volume of the mirror was considered as an objective for iterative optimization to obtain a topology optimization model. According to the results, a solid model was established, and its parameters were optimized. Finally, an integrated mirror structure with a total mass of 2.08 kg, root mean square of 5.9 nm, and lightweight ratio of 70% was obtained. Through comparisons to a contrast structure combined with a parameter optimization process, the validity of the topological structure features was determined, and the support characteristics were analyzed. A support structure consisting of a central hexagon and semi-closed structure contributes significantly to the improvement of surface shape accuracy under the conditions of self-weight. There is an optimal supporting position for the central hexagon structure, where the ratio of height to diameter of the regular hexagon is 0.26.