Abstract: GEO environmental degradation trend of 15years on solar absorptance for thermal control coatings such as S781 white paint, SR107-ZK white paint, silvered FEP, and OSR on the outer satellite are simulated by a combined low energy irradiation test. Severe degradation is found in organic white paint while OSR and silvered FEP remain quite stable. By comparison with flight test results, the effectiveness of the simulation method is shown. Based on the degradation trend data, the least squares regression method is used to obtain empirical formulas. The second order exponential decaying formulas are found quite good to fit degradation curves of four kinds of materials. Extrapolation for a longer test time is made and the results are verified. The error of using 8 years test results to extrapolate 15 year degradation is shown to be less than 1% .