Defect　engineering　is　a　highly　effective　approach　to　regulate　the　electronic　structure　of　the　catalyst　surface,　widely　employed　in　the　field　of　photocatalytic　energy　conversion.　In　this　study,　we　have　successfully　synthesized　a　novel　dual-defective　In2S3/Zn0.3Cd0.7S　(IS/ZCS)　heterojunction　structure　via　a　self-assembly　method,　composed　of　Zn-vacancy-rich　Zn0.3Cd0.7S　(ZCS)　and　S-vacancy-rich　In2S3　(IS).　Under　visible　light　illumination,　3%　IS/ZCS　sample　exhibits　remarkable　photocatalytic　performance　in　the　synergistic　reaction　of　CO2　reduction　and　4-chlor-obenzyl　alcohol　(Cl-PhCH2OH)　oxidation　with　the　CO　yield　significantly　improved　by　a　factor　of　3.5　and　51　compared　to　that　of　ZCS　and　IS,　respectively.　The　combined　experimental　data　and　theoretical　calculations　demonstrate　that　the　dual-defective　structure　and　Z-scheme　transfer　mode　are　the　key　factors　behind　the　enhanced　photocatalytic　activity,　providing　more　active　sites　and　effectively　improving　the　utilization　of　pho-togenerated　charge　carriers　(PCCs).　Moreover,　the　reaction　pathway　and　catalytic　mechanism　of　photocatalytic　CO2　reduction　were　elucidated　by　the　in-situ　FTIR　technique　combined　with　DFT　calculations,　monitoring　the　intermediate　and　final　products　during　the　reaction　period.　Our　results　provide　a　powerful　example　of　designing　novel　heterojunction　photocatalysts　with　high　activity　and　accelerating　the　separation　of　PCCs,　with　broad　implications　for　the　development　of　efficient　photocatalytic　systems.