The　construction　of　heterojunction　composites　can　effectively　inhibit　the　rapid　recombination　of　photogenerated　electron-hole　pairs　in　semiconductor　catalysts.　Further,　the　SPR　effects　of　noble　metal　can　promote　the　catalyst＇s　light　utilization　and　enhance　the　photothermal　conversion.　The　photothermal　synergy　effects　may　improve　the　CO2　reduction　ability　of　catalysts.　In　this　article,　Ag　particles　were　loaded　on　the　surfaces　of　BiOCl/Bi2WO6　heterojunction　catalysts　by　the　UV　light　reduction　method　to　successfully　construct　a　ternary　composite　catalyst　Ag/BiOCl/Bi2WO6.　The　catalyst　produces　CO　at　21.21　mu　mol/g/h　rate　and　CH4　at　6.41　mu　mol/g/h　rate　in　the　solid-gas　reaction　system　containing　CO2　and　H2O　vapor　under　the　300　W　Xe　lamp　irradiation.　The　CO　yield　is　7.6　and　16.1　times　that　of　the　pure　BiOCl　and　Bi2WO6,　respectively.　Moreover,　through　in　situ　infrared　spectroscopy,　photoelectrochemistry　and　UV-Vis　DRS　characterization,　the　intermediates,　charge　transfer　path　and　reaction　mechanism　of　CO2　reduction　with　water　vapor　were　explored.　The　efficient　electron　transfer　and　the　SPR　effect　of　Ag　synergistically　promote　the　photothermal　CO2　conversion　performance.　This　work　provides　some　new　insights　for　the　design　and　synthesis　of　Bi　based　catalysts　in　photothermal　catalytic　CO2　reduction　with　H2O　vapor.