The　construction　of　Z-scheme　heterojunctions　has　been　demonstrated　as　an　effective　strategy　to　improve　photocatalytic　hydrogen　(H2)　production　efficiency.　Herein,　a　Zn　vacancy　defect-mediated　direct　Z-scheme　CdS/ZnS　(CSZS-VZn)　heterojunction　was　developed　to　optimize　the　H2production　performance,　and　the　introduction　of　cation　defects　in　ZnS　could　regulate　the　band　structure　of　the　photocatalyst　by　forming　additional　energy　levels　within　the　band　gap　and　help　to　form　ohmic　contacts.　The　CSZS-VZnheterojunction　exhibited　a　H2evolution　rate　of　46.63　mmol　h−1g−1under　visible　light　illumination　in　an　aqueous　Na2S/Na2SO3system,　which　was　about　388　and　1727　times　higher　than　those　of　CdS　and　Zn-vacancy　ZnS　(ZnS-VZn),　respectively.　The　enhanced　photocatalytic　activity　of　CSZS-VZnwas　mainly　attributed　to　the　presence　of　Zn　vacancy　defects　upon　the　formation　of　the　Z-scheme　heterojunction　structure,　by　which　the　photogenerated　electrons　were　trapped　in　the　Zn　vacancy　defect　levels　of　ZnS　and　recombined　with　holes　in　the　valence　bands　of　CdS　at　heterojunction　interfaces　through　ohmic　contacts.　In　such　a　way,　electrons　in　the　conduction　bands　of　CdS　were　boosted　to　participate　in　H2evolution　reactions　and　photocorrosion　was　suppressed.　This　work　provides　a　viable　design　strategyviathe　engineering　of　cation　defects　in　Z-scheme　photocatalysts　for　photocatalytic　H2evolution.　©　The　Royal　Society　of　Chemistry　2021.