Photocatalysis provides an attractive strategy for synthesizing H2O2 at ambient condition. However, the photocatalytic synthesis of H2O2 is still limited due to the inefficiency of photocatalysts and decomposition of H2O2 during formation. Here, we report SnO2-TiO2 heterojunction photocatalysts for synthesizing H2O2 directly in aqueous solution. The SnO2 passivation suppresses the complexation and decomposition of H2O2 on TiO2. In addition, loading of Au cocatalyst on SnO2-TiO2 heterojunction further improves the production of H2O2. The in situ electron spin resonance study revealed that the formation of H2O2 is a stepwise single electron oxygen reduction reaction (ORR) for Au and SnO2 modified TiO2 photocatalysts. We demonstrate that it is feasible to enhance H2O2 formation and suppress H2O2 decomposition by surface passivation of the H2O2-decomposition-sensitive photocatalysts.