Defect　engineering,　heterojunction　construction　and　photo–thermal　synergy　are　efficient　means　to　improve　photocatalytic　performance.　Herein,　we　present　Co0.85Se　nanoparticles　in-situ　grown　on　sulfur　vacancy-rich　MnxCd1−xS　nanorods.　The　as-obtained　Co0.85Se/Mn0.3Cd0.7S　heterojunctions　achieved　H2-production　rate　of　46.7　mmol/h/g　at　5　,　which　is　14　times　higher　than　sulfur　vacancy-poor　Mn0.3Cd0.7S　and　better　than　1　wt%　Pt/Mn0.3Cd0.7S.　Sulfur　vacancies,　nonstoichiometric　Co0.85Se　and　Co0.85Se/MnxCd1−xS　heterojunctions　provide　more　active　sites,　harvest　light　and　speed　up　charge　carriers　transfer　for　photocatalytic　process.　Moreover,　elevating　reaction　temperature　can　decrease　charge-transfer　resistance,　promote　the　kinetics　for　reducing　H2O　to　H2,　and　thus　accelerate　H2-generation　rate　(up　to　79.7　mmol/h/g　at　25　).　The　apparent　quantum　yield　increases　from　29.3%　to　37.0%　when　the　reaction　temperature　rises　from　5　to　25　.　This　work　proposes　a　promising　strategy　for　the　application　of　sulfur　vacancy　and　nonstoichiometric　metal-selenide　cocatalyst　in　thermo-assisted　photocatalysis.　©　2021