With the development of space optical system, the technique of ultra thin mirror come forth and is paid more attention because of less difficulty in machining, low cost, lightweight, no disassembly during detecting and maintaining. The key technique takes advantage of deformation of ultra thin mirror as the influence of environment to adjust the surface figure. Its accuracy meets requirement. An analysis method is based on finite element analysis (FEA), and many items, including the amount of support points, the way of arrangement, the optimum design of support component are studied. The finite element method was used to analyze the mirror and some different mirror support schemes. The principal aim of the mirror analysis is to get numbers of support points and the ways of the support. There are three schemes including 12-6-1, 12-8-1 and 16-8-1models. Deformation of deadweight is calculated under the three conditions. The way of 16-8-1 is more suitable than the designs of other two. The support subassembly is amended to meet with the mirror surface RMS in the range of 30μm. Deformation of the mirror with support structure has been calculated. The result is 16.52nm, lower than a quarter of the wavelength, which indicates the feasibility of the support scheme applied to mirror. Theoretical result for the best way of support is presented. The result of analysis shows that requirement surface figure could be met through adjusting support points. It predicts feasibility of the support technique and provides theoretical value for active adjustment in the laboratory. At present, support and adjusting experiment of ultra thin mirror is being carried on.