Optimizing　the　local　surface　plasmon　resonance　(LSPR)　effect　of　non-noble　metals　through　alloying　has　been　crucial　for　improving　its　practical　application　in　the　field　of　photocatalysis.　Rare　studies　capture　the　detail　that　the　change　in　the　electronic　structure　of　metal　elements　caused　by　alloying　affects　plasma　carrier　concentration　and　the　local　surface　plasmon　resonance　effect.　Herein,　NiCuCoFe　medium-entropy　alloys　(MEAs)　nanoclusters　were　designed　and　used　to　modify　the　Bi3　O4　Br/CNNs　Z-scheme　heterojunction.　The　cocktail　effect　of　MEAs　causes　the　3d-orbital　hybridization　of　various　metal　elements,　which　promotes　the　release　of　charge　carriers.　The　higher　the　carrier　concentration,　the　stronger　the　LSPR　effect　of　MEAs.　In　addition,　the　mechanism　of　three　typical　working　pathways　of　the　LSPR　effect　to　improve　the　photocatalytic　performance　of　heterojunction　is　discussed.　And　compared　with　those　of　Bi3　O4　Br,　CNNs,　and　Bi3　O4　Br/CNNs,　the　rate　constant　of　MEAs-Bi3　O4　Br/CNNs　was　3.26,　11.16,　and　3.17　times　higher　during　the　degradation　of　norfloxacin,　respectively.　This　study　provides　a　new　strategy　for　understanding　the　mechanism　of　LSPR　and　the　rational　design　of　plasmonic　coupling　architectures　for　enhanced　photocatalysis.　(c)　2024　Published　by　Elsevier　Ltd　on　behalf　of　The　editorial　office　of　Journal　of　Materials　Science　&　Technology.