Construction　of　semiconductor　heterojunctions　with　matched　energy　band　alignment　is　an　efficient　strategy　to　boost　charge　separation,　thus　raising　photocatalytic　activity.　Developing　an　efficient　heterojunction　nanocomposite　free　from　noble　metal　is　of　critical　importance　for　visible-light-driven　photocatalysis.　Here,　NiSe　nanoparticles　were　used　to　construct　NiSe/Cd0.5Zn0.5S　p-n　heterojunction-based　nanocomposites　by　in　situ　chemical　deposition　method.　The　as-obtained　1%NiSe/Cd0.5Zn0.5S　nanocomposite　exhibits　good　durability　and　excellent　photocatalytic　hydrogen-generation　activity　of　78.01　mmol·h-1·g-1　with　visible　light,　which　is　almost　3　times　higher　than　that　of　Cd0.5Zn0.5S　and　outperforms　that　of　3　wt　%　Pt/Cd0.5Zn0.5S　(63.04　mmol·h-1·g-1).　The　highest　apparent　quantum　yield　measured　at　420　nm　reached　46%.　The　tight　contact　interface　and　p-n　junction　at　the　interface　of　NiSe　nanoparticles　and　Cd0.5Zn0.5S　can　efficiently　promote　charge　separation　and　migration,　and　thus　effectively　improve　photocatalytic　activity　as　well　as　the　utilization　of　solar　energy.　This　work　develops　an　efficient　noble-metal-free　CdxZn1-xS-based　heterojunction　nanocomposite　to　advance　solar　energy　harvesting.　Copyright　©　2020　American　Chemical　Society.