According to the aging phenomenon that di-methyl silicon oil working as a cooling material for liquid-immersed concentrating photovoltaic system for long time. In this paper, the method that enhances the weather-resistance of silicon oil by adding additives was proposed. Hydroxy-4-methoxy-benzophenone (UV-9) and a hindered amine light stabilizer named GW-783 were selected as additive to prepare composite materials. The performance of these composites was studied by accelerated life test (ALT). The results showed that the composites can inhibit the aging effect on flow and optic characteristics and did not affect the performance of solar cell. The most efficient one is the composite prepared by adding UV-9 and GW-783 together into silicon oil. (C) 2015 Elsevier Ltd. All rights reserved.