Crystalline　carbon　nitride　(CCN)-based　semiconductors　have　recently　attracted　widespread　attention　in　solar　energy　conversion.　However,　further　modifying　the　photocatalytic　ability　of　CCN　always　results　in　a　trade-off　between　high　crystallinity　and　good　photocatalytic　performance.　Herein,　a　facile　defect　engineering　strategy　was　demonstrated　to　modify　the　CCN　photocatalysts.　Results　confirmed　that　the　obtained　D-CCN　maintained　the　high　crystallinity;　additionally,　the　hydrogen　production　rate　of　D-CCN　was　approximately　8　times　higher　than　that　of　CCN.　Particularly,　it　could　produce　H2　even　if　the　incident　light　wavelength　extended　to　610　nm.　The　significantly　improved　photocatalytic　activity　could　be　ascribed　to　the　introduction　of　defects　into　the　CCN　polymer　network　to　form　the　midgap　states,　which　significantly　broadened　the　visible-light　absorption　range　and　accelerated　the　charge　separation　for　photoredox　catalysis.　©　2019　Wiley-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim