Photocatalytic　O-2　reduction　to　H2O2　is　a　green　and　promising　technology　with　advantages　in　cost-effectiveness,　sustainability,　and　environmental　friendliness,　but　its　efficiency　is　constrained　by　limited　selectivity　for　the　two-electron　oxygen　reduction　reaction　(ORR)　pathway.　Here,　we　anchored　isolated　Cu　atoms　with　tunable　oxidation　states　onto　WO3　as　effective　active　centers　to　enhance　photocatalytic　H2O2　production.　Due　to　the　charge　compensation　between　single　atoms　and　the　support,　the　oxidation　state　of　Cu　species　exhibited　a　loading-dependent　transition　between　+2　and　+1　valence.　Experimental　and　theoretical　analyses　indicate　that　Cu(I)　sites　exhibit　outstanding　O-2　adsorption　and　activation　capabilities,　transforming　the　thermodynamically　unfavorable　hydrogenation　of　the　*OOH　intermediate　(the　rate-determining　step　in　the　two-electron　ORR　pathway)　into　an　exothermic　process,　thereby　significantly　improving　selectivity　and　efficiency.　The　Cu(I)-SA/WO3　photocatalyst　exhibited　a　H2O2　production　rate　of　102　mu　mol　h(-1)　under　visible　light　irradiation,　much　higher　than　other　reported　photocatalysts.　More　importantly,　it　achieves　an　impressive　apparent　quantum　efficiency　of　30%　at　420　nm,　making　a　significant　breakthrough　in　this　field.　This　work　provides　novel　perspectives　for　designing　single-atom　catalysts　for　efficient　H2O2　synthesis　via　electronic　state　modulation.