S-scheme　heterojunction　has　attracted　much　attention　due　to　its　unique　structure　and　interface　interaction.　Herein,　AgBr/BiOBr　heterojunction　with　surface　oxygen　vacancies　(OVs)　was　in　situ　synthesized　by　a　facile　chemical　method.　It　was　found　that　the　evolution　rates　of　photoreduction　of　CO2　to　CO　and　CH4　with　0.33AB　are　212.6　and　5.7　mu　mol　g(-1)　h(-1)　respectively,　which　are　9.2　and　5.2　times　higher　than　those　of　pure　BiOBr.　It　was　demonstrated　that　the　S-scheme　band　structure　could　improve　the　utilization　of　sunlight,　increase　the　reduction　power　of　photogenerated　electrons,　and　enhance　the　separation　and　transfer　of　photogenerated　charge　carriers.　Furthermore,　the　OVs　on　the　surface　of　BiOBr　for　AgBr/BiOBr　heterojunction　are　conductive　to　the　adsorption　and　activation　of　CO2　molecules.　The　synergetic　effect　of　S-scheme　band　structure　and　OVs　on　photocatalytic　reduction　of　CO2　was　discussed.　The　work　provides　a　facile　method　for　in　situ　construction　of　S-scheme　heterojunction　with　defect　for　CO2　photoreduction.