Hydrogen peroxide (H2O2) is an important chemical as it is an environmentally friendly oxidant for organic synthesis and environmental remediation as well as a promising candidate for the liquid fuel. Photocatalytic generation of H2O2 is sustainable, and many efforts have been put into the development of new catalysts to gain high H2O2 yields. In this investigation, Au/ZnO, Ag/ZnO and Au-Ag/ZnO catalysts were prepared by the simultaneous impregnation of HAuCl4 and AgNO3 and they were used to generate H2O2 from a methanol/O2 system. It was demonstrated that Au/ZnO had the best performance at generating H2O2. The presence of Au on ZnO accelerated the generation of H2O2 on ZnO and facilitated H2O2 adsorption onto the catalyst surface, which resulted in the reaction kinetics changing from zero-order to first-order. Ag atoms on Ag/ZnO were unstable and would strip from the surface of ZnO during irradiation, decreasing the yield of H2O2. The stabilization of Ag on Au-Ag/ZnO depended on the ratio of Au and Ag. Au0.1Ag0.2/ZnO was a stable catalyst and it showed that the presence of Ag promoted the formation and decomposition of peroxide, simultaneously.