Highly　dispersed　Cu2O　clusters　loaded　on　TiO2　nanosheets　with　dominant　exposed　{001}　facets　are　prepared　by　a　hydrothermal　treatment　followed　by　photodeposition.　The　physicochemical　properties　of　the　as-prepared　samples　are　characterized　carefully.　The　deposition　position　and　chemical　state　of　the　Cu2O　clusters　are　characterized　by　X-ray　diffraction,　transmission　electron　microscopy,　UV-vis　diffuse　reflectance　spectroscopy,　EPR　spectroscopy,　and　in　situ　CO-adsorbed　FTIR　spectroscopy,　respectively.　The　results　show　that　in　situ　Cu　deposition　leads　to　in　situ　formation　of　abundant　oxygen　vacancies　(V-o)　on　the　surface　of　the　TiO2　nanosheets.　Interestingly,　the　co-existence　of　V-o　and　Cu2O　clusters　could　promote　the　photoactivity　of　CO2　reduction　efficiently.　The　surface　V-o　play　a　significant　role　in　the　reduction　of　CO2.　Meanwhile,　the　deposited　Cu(I)　species　serve　also　as　active　sites　for　the　formation　of　CH4,　and　then　protect　CH4　from　degradation　by　generated　oxidation　species.　For　the　photoreduction　of　CO2　to　CH4,　it　is　found　that　the　content　level　of　Cu2O　has　a　significant　influence　on　the　activity.　Cu-TiO2-1.0　shows　the　highest　photocatalytic　activity,　which　is　over　30　times　higher　than　that　of　the　parent　TiO2.　This　great　enhancement　of　photocatalytic　activity　may　be　contributed　by　high　CO2　adsorption　capacity,　high　electron　mobility,　and　high　concentration　of　V-o.　However,　the　effect　of　the　surface　area　of　the　samples　on　the　activity　is　negligible.　All　of　this　evidence　is　obtained　by　CO2-sorption,　electrochemistry,　in　situ　FTIR　spectroscopy,　in　situ　ERP　techniques,　etc.　The　reaction　intermediates　are　detected　by　in　situ　FTIR　spectroscopy.　Finally,　a　probable　mechanism　is　proposed　based　on　the　experimental　results.　It　is　hoped　that　our　work　could　render　one　of　the　most　effective　strategies　to　achieve　advanced　properties　over　photofunctional　materials　for　solar　energy　conversion　of　CO2.