Abstract: This paper introduces a study of 15 years geostationary environmental effects on solar absorptance degradation at outer surface of satellite, in order to supply reliable bases for thermal control design and material selection. A kind of combined low energy irradiation simulation test methods is studied. A combined low energy environment simulation test facility and a solar absorptance in-situ measuring system developed by CAST is briefly introduced. A long-term solar absorptance degradation simulation test of satellite thermal control coatings such as S781 white paint, SR107-ZK white paint, silvered F46, OSR etc is carried out on that facility. The test data for 15 years environmental effects on solar absorptance degradation of these thermal control coatings are obtained. The comparison between the simulation test and flight test are made to prove the reality of the simulation.