The　Coulomb　interactions　between　excited　electrons　and　holes　have　a　very　important　influence　on　the　photo-physical　processes　in　2D　semiconductors.　Exciton　dissociation　is　one　of　the　key　steps　that　significantly　contribute　to　the　efficiency　of　photocatalysis,　but　its　research　in　the　relevant　aspects　of　photocatalysis　has　not　been　in-depth.　Herein,　the　BP/TiO2　heterojunction　as　a　prototypical　model　system　was　constructed　on　the　surface　of　urchin-like　TiO2　where　black　phosphorous　(BP)　quantum　dots　(QDs)　grew.　The　BP/TiO2　heterojunction　exhibits　an　improved　H-2-production　rate　of　112　mu　mol.h(-1).g(-1)　under　UV-visible　light　irradiation　without　any　cocatalysts,　which　is　2.4　times　higher　than　that　of　pure　TiO2　(47　mu　mol.h(-1).g(-1)).　As　a　typical　exciton-rich　material,　BP　QDs　have　special　advantages　on　the　charge　separation　process,　because　of　their　prominent　many-body　effect,　short　carrier　transport　distance,　and　large　specific　surface　with　rich　reactive　sites.　The　energy　difference　between　the　con-duction　bands　turns　out　to　be　the　driving　force　for　exciton　dissociation　in　the　BP/TiO2　heterojunction.　The　theoretical　calculation　implies　that　the　excited　electron　tends　to　transfer　from　BP　QD　to　TiO2.　The　high　catalytic　performance　of　heterojunction　contributes　to　the　effective　exciton　dissociation,　interfacial　charge　separation,　and　charge-carrier　accumulation.　This　work　lays　the　foundation　for　the　design　of　the　BP　QDs　based　photocatalytic　system　and　its　application　in　photocatalytic　hydrogen　production　and　provides　an　effective　reference　for　increasing　the　active　sites　of　heterojunctions.