A　photocatalyst　composed　of　Ag　nanoparticles　(NPs)　supported　on　pseudo-hexagonal　niobium　pentoxide　(TTNb2O5)　was　synthesized　in　this　study.　This　catalyst　exhibited　an　enhanced　photocatalytic　performance　for　the　reduction　of　CO2　by　H2O　under　UV-vis　light　irradiation.　A　CO　yield　of　up　to　66.5　mu　mol　center　dot　g　(-1)center　dot　h　(-1)　with　a　selectivity　of　92.1%　were　achieved,　and　also　an　excellent　stability　was　observed　across　four　cycles.　Characterization　studies　show　that　the　introduction　of　Ag　NPs　onto　Nb2O5　was　beneficial　for　the　formation　of　oxygen　vacancies　(Vos)　(which　were　further　regenerated　when　exposed　to　UV　light),　resulting　in　the　enhanced　adsorption　and　activation　of　CO2.　The　electron-rich　Ag　NPs　were　conducive　to　the　formation　of　Ag-H　bonds　after　the　dissociation　of　H2O　to　H+,　which　promoted　the　proton-electron　coupling　process　for　converting　the　CO2　absorbed　at　Vos　sites　into　CO.　Moreover,　the　localized　surface　plasmon　resonance　(LSPR)　of　Ag　NPs,which　was　induced　by　visible　light,　playing　a　role　in　accelerating　the　decomposition　and　desorption　of　*COOH　into　CO.　This　work　provides　new　insight　into　reduction　of　CO2　by　H2O　under　UV-vis　light　irradiation.