In this paper, porous microsphere Ag-ZnO photocatalyst was prepared and used in photocatalytic degrading of methane and ethylene at room temperature. The Ag-ZnO photocatalyst showed good stability and high efficiency under the simulated sunlight. Both methane and ethylene can be oxidized into CO2. In the photocatalytic reactions, the decorating of Ag nanoparticles plays key roles in promoting the separation of photo-generated carriers, promoting the oxygen reduction process and realizing the complete mineralization of gas molecules.