Inefficient　charge　separation　and　insufficient　surface　catalytic　sites　remain　the　main　impediment　in　developing　highly　efficient　and　selective　catalysts　for　CO2　photoreduction.　Surface　defects　are　effective,　but　their　function　is　always　constrained　within　the　defect　location.　Herein,　a　desirable　surface　cation　vacancy　strategy　is　implemented　to　solve　the　above　obstacles　over　Bi4Ti3O12　nanosheets.　The　surface　Ti　vacancy　(V-Ti)　creates　an　atomic-level　charge　transfer　channel　on　the　surface　of　Bi4Ti3O12,　allowing　a　rapid　transfer　of　photon-generated　electrons　from　the　V-Ti　site　of　neighboring　Ti　and　O　atoms　to　CO2　molecules.　More　importantly,　V-Ti　activates　neighboring　Ti　and　O　atoms,　which　allows　them　a　stronger　ability　for　enhancing　CO2　adsorption　and　conversion.　Thus,　a　convenient　and　swift　charge　transfer　channel　and　activated　near　surface　region　are　formed　on　the　surface　of　Bi4Ti3O12,　profoundly　boosting　the　CO2　reduction　process,　as　evidenced　by　experimental　and　theoretical　results　collectively.　Without　any　sacrificial　agents　or　cocatalysts,　Bi4Ti3O12　with　an　optimal　V-Ti　concentration　exhibits　an　outstanding　CO　production　rate　of　15.17　mu　mol　g(-1)　h(-1),　nearly　5　times　higher　than　that　of　pristine　Bi4Ti3O12.　This　work　unfolds　a　new　function　of　surface　cation　vacancies　to　substantially　enhance　CO2　photoreduction.