The　direct　hybridization　of　Pt　and　g-C3N4　generally　forms　a　Schottky　barrier　between　the　two　components,　which　unavoidably　hinders　the　migration　of　photogenerated　electrons　from　g-C3N4　to　the　Pt　cocatalyst.　Herein,　we　report　the　first　efficient　allochroic　Pt/g-C3N4　photocatalyst　that　can　form　an　ohmic　contact　through　photoconversion　of　semiconducting　g-C3N4　to　metalloid,　accompanied　with　the　charge　carrier　storage　and　photocatalyst　color　change,　which　is　proved　experimentally　and　theoretically.　Through　intermittent　exposure　of　Pt/gC3N4　photocatalyst　to　air　for　a　few　minutes　during　photocatalysis,　the　photocatalyst　shows　the　highest　hydrogen　evolution　performances.　The　ohmic　contacts　greatly　promote　the　electron　transfer　from　the　semiconducting　gC3N4　to　the　Pt　cocatalyst　driven　by　the　built-in　electric　field.　In　addition,　the　mechanism　for　the　photocatalyst　deactivation　and　activation　is　presented.　The　compositional　tuning　of　the　allochroic　g-C3N4　through　light　irradiation　and　exposure　to　air　can　control　over　the　photocatalytic　activity　and　long-term　stability　for　hydrogen　evolution.　This　report　for　the　first　time　unveils　the　deactivation　and　regeneration　mechanisms　of　SCN.