Abstract: Experiments are conducted with the ground analog equipments to investigate the effect of atomic oxygen and ultraviolet on silicone rubber O rings. By measuring the pressure between two O rings, leakage rates before and after exposure to atomic oxygen or ultraviolet are compared . In addition,the surface characteristics of O ring are analyzed by scanning electron microscope . All experiments prove that the surface characteristics and leakage rate of an O ring are affected seriously when it is exposed to atomic oxygen and ultraviolet.