In order to satisfy the stringent requirement for high surface shape accuracy and thermal stability of large-aperture mirrors in the complex space environment, a lightweight design for a Φ660 mm-diameter mirror was carried out. A method for creating the initial structure of the mirror using the classical theoretical formula, combining sensitivity analysis and parameter optimization for comprehensive design was proposed. Firstly, the parametric model was established, the influence law of the structure parameters of the mirror on the surface shape change was studied, and then iterations for the structural parameters with high sensitivity to the mirror surface RMS value were optimized through sensitivity analysis. Compared with the traditional mirror design model, this method reduced the optimization design space, saved computational cost and time, could globally optimize in the design space, and converged quickly to the optimal value. The mass of optimized mirror was 13.6 kg and the lightweight rate of the mirror reached 78.4%. The PV value of mirror surface accuracy was less than ?姿/10 and RMS value was less ?姿/40(λ=632.8 nm) under gravity load. The first-order frequency 121 Hz of the mirror assembly met the dynamic stiffness requirements of the mirror. Finally, based on the optimized results, the optimal mirror was put into production.