Abstract: The radiative properties of thermal control coatings are important parameters in the thermal control design of spacecraft. On the basis of analyzing the absorbing and reflecting process of the second surface mirror of plastics, a radiative model is established. By combining the radiative model with the apparent radiative parameters such as the solar absorption and the infrared emissivity, the surface reflectivity and the medium absorption coefficient are obtained by the non-linear least squares method. The effects of thickness on the solar absorptivity and the infrared emissivity of the thermal control coatings are analyzed. The reflectivity and the absorption coefficient of the Kapton film are calculated to be 0.571 and 19.343 mm-1 for the solar spectrum, and those for the infrared spectrum are 0.227 and 39.615 mm^-1. The reflectivity and the absorption coefficient of the F46 film are 0.744 and 0.757 mm^-1 for the solar spectrum, and those for the infrared spectrum are 0.111 and 9.240 mm^-1.