As　a　sustainable　technology,　semiconductor　photocatalysis　has　attracted　considerable　interest　in　the　past　decades　owing　to　its　potential　to　relieve　energy　and　environmental　issues.　By　virtue　of　their　unique　structural　and　electronic　properties,　emerging　ultrathin　2D　materials　show　enormous　potential　to　achieve　efficient　photocatalytic　performance.　Herein,　we　report　the　fabrication　of　2D/2D　ZnxCd1-xIn2S4/g-C3N4　heterostructure　via　a　facile　hydrothermal　method　for　visible-light-driven　photocatalytic　H-2　evolution.　By　tailoring　the　energy　band　structure　of　the　ZnxCd1-xIn2S4　solid　solutions,　the　position　of　conduction　band　can　be　largely　elevated　and　thus　achieve　a　strong　photoreduction　capability.　A　further　construction　of　2D/2D　ZnxCd1-xIn2S4/g-C3N4　heterojunction　can　reduce　charge　transfer　distance　from　inner　part　to　surface　and　create　abundant　interfacial　charge　transfer　pathways,　resulting　in　significantly　boosted　migration　and　separation　efficiency　of　photogenerated　charge　carriers.　Consequently,　this　energy　band　engineering　effect　combined　with　the　advantages　of　the　unique　2D/2D　architecture　endows　the　ZnxCd1-xIn2S4/g-C3N4　heterojunction　with　a　remarkable　H2　evolution　rate　of　170.3　mu　mol　h(-1)　under　visible-light　irradiation　(lambda　＞　420　nm)　in　the　absence　of　co-catalyst,　which　is　nearly　4.5　and　567.7　times　that　of　Zn1/2Cd1/2In2S4/CN　(37.8　mu　mol　h(-1))　and　pure　g-C3N4　(0.3　mu　mol　h(-1)),　respectively.　Furthermore,　the　apparent　quantum　yield　(AQY)　and　the　solar-to-hydrogen　(STH)　energy　conversion　efficiency　over　Zn1/2Cd1/2In2S4/CN　are　8.5%　and　2.6%,　respectively.　This　study　sheds　light　on　the　potential　of　integrating　the　two　strategies　of　energy　band　modulation　and　2D/2D　heterojunction　into　designing　semiconductor　photo-catalysts　for　highly　efficient　solar-to-energy　conversion　applications.