Abstract: Based on Kirchhoff’s law and optical thin film theory,the Macleod software is used to investigate the effect of the material and structure of radiant cooling films on the cooling performance. The radiant cooling film requires high reflectivity in the solar band of 0.3-3.0 μm to prevent the object from heat gain. It also requires a high emissivity in the infrared band of 8-13 μm,which lowers its own temperature. It is found that SiO₂ has a low reflectance in the 8-13 μm band and a high reflectance in other bands,making it be an ideal material for the fabrication of radiation cooling films. The composite film formed by the superposition of high molecular polymer PS and SiO₂ will produce the resonance phenomenon of phonon-polaron excitation in the 8-13 μm band,which can further reduce the reflectivity. Therefore,PS is an effective auxiliary material for improving the performance of radiation cooling films. After optimization by Simplex method,the radiant cooling film is combined with SiO₂-PS-SiO₂ structure. When the thickness of each layer is 0.2 μm,0.8μm and 70 μm,repectively,the radiation force is as high as 136.2 W/m~2,and the average emissivity reaches 92.12%.