Heterojunction　structure　of　the　composite　photocatalyst　with　the　intimate　interface　and　sufficient　contact　areas　is　the　key　to　achieve　superior　photogenerated　charge　carriers　migration　efficiency.　However,　it　still　remains　a　great　challenge.　Herein,　a　novel　ZnIn2S4/HNb3O8　heterojunction　with　a　strong　Nb-S　bond　connected　2D/2D　in-plane　interface　is　successfully　fabricated　via　a　two-step　synthesis　method.　Due　to　the　similarity　of　the　chemical　property,　S　precursors　for　ZnIn2S4　are　preferred　trapped　by　the　O　defects　on　HNb3O8,　which　induce　the　formation　of　Nb-S　bond　in　the　2D/2D　interface　under　the　hydrothermal　process.　The　unique　2D/2D　structure　endows　the　heterojunction　with　large　interfacial　area　and　the　Nb-S　bond　as　high-speed　channels　facilitate　the　interfacial　electrons　transfer.　Furthermore,　Kelvin　probe　test　demonstrates　an　interfacial　electric　field　oriented　from　HNb3O8　to　ZnIn2S4　is　formed　as　driving　force　for　the　interface　charge　transfer.　As　a　result,　the　photoexcited　electrons　may　directionally　migrate　across　the　interface,　thereby　promoting　the　photocatalytic　activity.　The　optimal　H2　evolution　amount　reaches　95.2　mmol　g−1,　corresponding　to　10.8　times　of　ZnIn2S4.　The　in-situ　construction　of　chemical　bonded　heterojunction　will　provide　a　reference　for　designing　high-efficiency　heterojunction　photocatalyst.　©　2021　The　Author(s)