Constructing　a　Z-scheme　heterojunction　with　enhanced　photocatalytic　hydrogen　evolution　for　graphitic　carbon　nitride-based　(g-C3N4)　composites　is　challenging　because　integrating　g-C3N4　with　other　semiconductors,　without　specific　band　structure　design,　typically　results　in　type　I　or　type　II　heterojunctions.　These　heterojunctions　have　lower　redox　ability　and　limited　enhancement　in　photocatalysis.　Herein,　we　select　highly　crystalline　carbon　nitride　(HCCN)　as　a　proof-of-concept　substrate.　For　the　first　time,　we　develop　a　AgBr　nanosphere/HCCN　composite　photocatalyst　that　features　an　all-solid-state　direct　Z-scheme　heterojunction　for　visible-light　photocatalytic　hydrogen　evolution.　The　electron　transfer　mechanism　is　initially　studied　from　the　band　structures　and　Fermi　levels　of　HCCN　and　AgBr.　It　is　subsequently　confirmed　by　X-ray　photoelectron　spectroscopy　(XPS),　and　electron　microscopy.　The　close　heterojunction　contact　and　the　built-in　electron　field　of　the　Z-scheme　heterojunction　promote　the　migration　and　separation　of　photogenerated　electrons　and　holes　in　the　composite　photocatalyst.　Due　to　the　redistribution　of　charge　carriers,　the　photocatalyst　shows　superior　redox　capability　and　a　markedly　enhanced　hydrogen　evolution　performance　compared　to　its　individual　components.　Combining　all　the　advantages,　AgBr　nanosphere/HCCN　reached　an　apparent　quantum　efficiency　(AQE)　of　6　%　under　the　illumination　of　410　nm,　which　is　4　times　higher　than　that　of　the　single　HCCN　component.　©　2024　The　Author(s)