The　construction　of　heterojunctions　is　a　promising　manner　to　accelerate　the　separation　and　transfer　of　the　charge　carriers　at　the　interface.　Herein,　a　binary　poly(heptazine-triazine)　imides　(PHI/PTI)　with　semi-coherent　interfaces　was　fabricated　via　a　facile　two-step　salt-melt　synthetic　process.　The　built-in　electric　fields　at　the　semi-coherent　interface　endow　prompt　exciton　splitting　and　charge　carrier　separation.　Hence,　the　optimized　PHI/PTI-based　copolymer　presents　a　high　apparent　quantum　yield　(AQY=64　%)　for　visible-light　driven　hydrogen　production,　by　the　aids　of　K2HPO4　as　charge　transfer　mediator.　This　study　provides　physical　insights　for　the　rational　promotion　of　the　photocatalytic　performance　from　the　viewpoint　of　interfacial　engineering　of　photocatalytic　junctions　on　crystalline　carbon　nitride　based　semiconductors.　©　2022　Wiley-VCH　GmbH.