For the requirements of the mirror in a large-aperture spaceborne telescope for lightweight , a web-skin-typed ground structure based topology optimization method was presented for the configuration design of large-aperture mirror. Based on the idea of topology optimization, the ground structure in this method was restricted to be a web-skin-type structure composed of a surface (skin) stiffened by webs, and the change of the configuration was described by whether webs or parts of the webs were deleted from the ground structure or not. Firstly, the web-skin-type ground structure was discreted with shell elements, the relative densities of all the elements on the webs were taken as design variables (the relative density was taken as 1 or 0 to describe whether the webs or parts of webs were kept or not).Then, by using optical aberration of the mirror in the load case of vertical optical axis as a design restraint, and the total weight of the structure as a optimized target, a topology optimization model was established. Furthermore, the concept configuration based on the structure obtained by topology optimization was extracted. Finally, the dynamic and static stiffnesses and optical performance of the mirror were analyzed using the finite element method, the mirror configuration was modified, and a lightweight mirror structural innovation configuration was obtained. It shows that the optical aberration PV and RMS of the mirror obtained by the design example are less than λ/10 and λ/40, respectively, the fundamental frequency is greater than 1 000 Hz and the lightweight ratio reaches 86.0%. The results demonstrate the validity of the proposed approach properly.