Graphitic　carbon　nitride　(g-C3N4)　is　an　attractive　photocatalyst　for　solar　energy　conversion　due　to　its　unique　electronic　structure　and　chemical　stability.　However,　g-C3N4　generally　suffers　from　insufficient　light　absorption　and　rapid　compounding　of　photogenerated　charges.　The　introduction　of　defects　and　atomic　doping　can　optimize　the　electronic　structure　of　g-C3N4　and　improve　the　light　absorption　and　carrier　separation　efficiency.　Herein,　the　high　efficiency　of　carbon　nitride　photocatalysis　for　hydrogen　evolution　in　visible　light　is　achieved　by　an　S-modified　double-deficient　site　strategy.　Defect　engineering　forms　abundant　unsaturated　sites　and　cyano　(─C≡N),　which　promotes　strong　interlayer　C─N　bonding　interactions　and　accelerates　charge　transport　in　g-C3N4.　S　doping　tunes　the　electronic　structure　of　the　semiconductors,　and　the　formation　of　C─S─C　bonds　optimizes　the　electron-transfer　paths　of　the　C─N　bonding,　which　enhances　the　absorption　of　visible　light.　Meanwhile,-C≡N　acts　as　an　electron　trap　to　capture　photoexcited　electrons,　providing　the　active　site　for　the　reduction　of　H+　to　hydrogen.　The　photocatalytic　hydrogen　evolution　efficiency　of　SDCN　(1613.5 µmol g−1 h−1)　is　31.5　times　higher　than　that　of　pristine　MCN　(51.2 µmol g−1 h−1).　The　charge　separation　situation　and　charge　transfer　mechanism　of　the　photocatalysts　are　investigated　in　detail　by　a　combination　of　experimental　and　theoretical　calculations.　©　2024　Wiley-VCH　GmbH.