Photocatalytic production of hydrogen peroxide (H₂O₂) is an ideal pathway for obtaining solar fuels. Herein, an S-scheme heterojunction is constructed in hybrid TiO₂/In₂S₃ photocatalyst, which greatly promotes the separation of photogenerated carriers to foster efficient H₂O₂ evolution. These composite photocatalysts show a high H₂O₂ yield of 376 μmol/(L·h). The mechanism of charge transfer and separation within the S-scheme heterojunction is well studied by computational methods and experiments. Density functional theory and in-situ irradiated X-ray photoelectron spectroscopy results reveal distinct features of the S-scheme heterojunction in the TiO₂/In₂S₃ hybrids and demonstrate charge transfer mechanisms. The density functional theory calculation and electron paramagnetic resonance results suggest that O₂ reduction to H₂O₂ follows stepwise one-electron processes. In₂S₃ shows a much stronger interaction with O₂ than TiO₂ as well as a higher reduction ability, serving as the active sites for H₂O₂ generation. The work provides a novel design of S-scheme photocatalyst with high H₂O₂ evolution efficiency and mechanistically demonstrates the improved separation of charge carriers.