Abstract: The solar absorptance (αs) degradations of S781 and the SR107 white coatings after a combined radiation are discussed in this paper. The morphologies and the chemical compositions of the both samples are analyzed by using the scanning electronic microscope (SEM) and the X-ray photoelectron spectra (XPS). A forecasting model is employed to predict the αs changes of the both samples in the combined radiation environment. It is shown that the chemical compositions of SR107 coated with methyl silicone rubber binder see little changes before and after the radiation. Great cracks appear on the surface of S781 coatings, the chemical compositions of which are also changed. Though the αs of SR107 gets to a stable value much more quickly during the radiation, the αs degradation of SR107 is more severe than that of S781.