Ultrathin　TiO2　nanosheet　(NST)　with　abundant　Ti3+　sites　is　developed　as　a　photocatalyst　which　exhibits　a　high　yield　(147.2　mu　mol　g(-1)　h(-1))　and　selectivity　(96.8%)　for　CO2　to　CH4.　The　results　of　in　situ　FTIR,　in　situ　EPR　and　density　functional　theory　(DFT)　calculation　suggest　that　CO2　would　be　selectively　activated　on　NST　surface　via　forming　the　bridging　Ti　center　dot　center　dot　center　dot　CO2-center　dot　center　dot　center　dot　Ti　coordination　species　which　not　only　lowers　the　activation　energy　barrier,　but　also　determines　the　selectivity　of　CH4.　Additionally,　NST　with　the　better　separation　and　transfer　ability　for　photogenerated　electrons-holes　can　fleetly　supply　the　electrons　to　CO2　molecules　for　high　efficiently　producing　CH4　via　the　Ti-C　coordination　bond.　Finally,　a　possible　mechanism　of　the　synergistic　effect　about　coordination-activation　and　photocatalysis　is　discussed　at　a　molecule　level.　This　work　would　offer　a　perspective　for　designing　an　effective　photocatalyst　and　tailoring　the　selectivity　of　products　by　coordination　activation.