Abstract: In order to explore a method to characterize the service behavior of thermal control coatings in geostationary earth orbit (GEO), evolution in optical properties of Teflon FEP/Al second surface mirror was investigated in the conditions of independent radiation with electrons and/or protons and combined radiation with electrons with solar electromagnetic rays. Experimental results show that the electron radiation would result in an accumulation of negative charges on the surface of Teflon FEP/Al coatings, which might obstruct the experimental results and can be reduced to a quite extent by the simultaneous radiation of solar electromagnetic rays. Under the condition of the same multiplier values of fluence and energy (φE), the increment of solar absorptance (Δas) of Teflon FEP/Al coatings