Abstract: SiC particle reinforced aluminum matrix composites are expected to be used as structural materials of the next generation space camera, due to their lightweight, high modulus, high thermal conductivity and low expansion coefficient. In this paper, several space environmental simulation tests, including the temperature cycling, the particle irradiation, the atomic oxygen irradiation and the vacuum-ultraviolet irradiation, are carried out for the SiC_p/2009 aluminum matrix composites. The mechanical and physical properties of the composites are determined before and after the tests. The results show that before and after these space environment simulation tests, the yield strength, the tensile strength and the elastic modulus are changed no more than 2%, the average linear expansion coefficient is changed no more than 1×10^-6 ℃^-1, but the thermal conductivity and the specific heat capacity are each decreased by a maximum of 17% and 28%. Then a comparative study of different environmental effects on the mechanical and physical properties of the SiC_p/2009 aluminum matrix composites and the internal mechanism of significant changes of the specific heat capacity and the thermal conductivity is briefly discussed. A model involving the stress affected zone (SAZ) around the SiC particles, the cumulative damages on the surface or inside the material during the irradiation tests and the inevitable voids inside the material because of the powder metallurgy process are proposed to explain the significant change of specific heat capacity and thermal conductivity before and after these space environment simulation tests.