Photocatalytic　conversion　of　CO2　into　fuels　using　pure　water　as　the　proton　source　is　of　immense　potential　in　simultaneously　addressing　the　climate-change　crisis　and　realizing　a　carbon-neutral　economy.　Single-atom　photocatalysts　with　tunable　local　atomic　configurations　and　unique　electronic　properties　have　exhibited　outstanding　catalytic　performance　in　the　past　decade.　However,　given　their　single-site　features　they　are　usually　only　amenable　to　activations　involving　single　molecules.　For　CO2　photoreduction　entailing　complex　activation　and　dissociation　process,　designing　multiple　active　sites　on　a　photocatalyst　for　both　CO2　reduction　and　H2O　dissociation　simultaneously　is　still　a　daunting　challenge.　Herein,　it　is　precisely　construct　Cu　single-atom　centers　and　two-coordinated　N　vacancies　as　dual　active　sites　on　CN　(Cu-1/N2CV-CN).　Experimental　and　theoretical　results　show　that　Cu　single-atom　centers　promote　CO2　chemisorption　and　activation　via　accumulating　photogenerated　electrons,　and　the　N2CV　sites　enhance　the　dissociation　of　H2O,　thereby　facilitating　the　conversion　from　COO*　to　COOH*.　Benefiting　from　the　dual-functional　sites,　the　Cu-1/N2CV-CN　exhibits　a　high　selectivity　(98.50%)　and　decent　CO　production　rate　of　11.12　mu　mol　g(-1)　h(-1).　An　ingenious　atomic-level　design　provides　a　platform　for　precisely　integrating　the　modified　catalyst　with　the　deterministic　identification　of　the　electronic　property　during　CO2　photoreduction　process.