H2S　selective　catalytic　oxidation　via　photocatalysis　is　a　low-cost　and　efficient　approach.　Herein,　we　modeled　a　(CoP)4　cluster　loaded　melon-based　carbon　nitride　to　represent　experimental　cobalt　phosphate　cocatalyst　adsorption　on　polymeric　carbon　nitride　for　revealing　the　mechanism　of　H2S　selective　catalytic　oxidation　to　SO2　via　the　density　functional　theory　(DFT)　calculations.　Due　to　the　hydrogen　bond　effect,　the　calculated　results　show　that　H2S　selective　oxidation　prefers　to　occur　through　the　quasi　Mars-van　Krevelen　(quasi-MvK)　mechanism　rather　than　Langmuir-Hinshelwood　(LH)　mechanism　according　to　the　thermodynamic　perspective,　in　which　quasi-MvK　mechanism　exhibits　a　favorable　limiting　potential　of　0.26　V.　Overall,　this　work　offers　a　basic　understanding　for　microscopic　mechanism　of　H2S　catalytic　oxidation.