In recent years, lighting simulation equipment used in space environment simulation has attracted much attention, including solar lighting simulators, light array lighting simulators, infrared heating cages and so on. Solar illumination simulation equipment mainly includes lamp room, integrator, window, mirror, etc. Because of the particularity of vertical illumination simulation structure, the metal mirror needs to adopt hanging structure. Combined with the characteristics of high irradiation and high heat energy of illumination simulation system, it will produce higher heat radiation energy on the surface of metal mirror. The temperature uniformity and thermal deformation index under the load are very important to the irradiation uniformity of illumination simulation equipment, that is, the high irradiation hanging metal mirror has high requirements for thermal stability.The thermal stability of the hanging meter-level metal mirror used in high irradiation environment simulation equipment was systematically analyzed, and the thermal stability analysis of the single meter-level metal mirror used in vertical illumination simulation equipment was mainly conducted, including thermal simulation verification and analysis, mechanical simulation analysis and optical simulation analysis. Finally, the structure illumination simulation equipment. The proposed thermal stability analysis method provides a guiding method for the structural design of the hanging metal mirror, a key component in the subsequent high irradiation vertical illumination simulation equipment.