The photocatalytic reduction of carbon dioxide (CO2) to methane (CH4) represents a sustainable route for directly converting greenhouse gases into chemicals but poses a significant challenge in achieving high selectivity due to thermodynamic and kinetic limitations during the reaction process. This work establishes Ru-OV active sites on the surface of TiO2 by anchoring coordination unsaturated Ru single-atoms, which stabilize crucial reaction intermediates and facilitate local mass transfer to achieve dual optimization of the thermodynamics and kinetics of the overall photocatalytic CO2reduction. Combining operando spectroscopy with density functional theory (DFT) calculations indicates that oxygen vacancies (OV) inhibits the desorption of *CO, whereas Ru facilitates proton extraction. This configuration not only lowers the overall activation energy barrier but has also been engineered to serve as a selectivity switch, changing the reaction route to produce CH4 instead of CO. Consequently, the Ru-OV/TiO2exhibits a 195.4-fold improvement in the CH4 yield compared to TiO2, accompanied by an increase in selectivity to 81%.