Photocatalytic　CO2　reduction　reaction　(CO2RR)　is　a　desired　solution　to　overcome　current　energy　and　environmental　problems.　As　a　main　competitive　reaction,　hydrogen　evolution　reaction　(HER)　urgently　needs　to　be　restrained　to　improve　the　conversion　rate　and　selectivity　of　CO2RR.　Here,　we　report　a　Cu2O/MXene-g-C3N4　(Cu2O/MX-CN)　p-n　heterojunction　that　achieves　highly　selective　CO2　reduction　of　93%　(competing　with　HER)　under　visible　light.　CO　is　the　only　product　of　CO2RR,　which　yielded　28.4　mu　mol　g(-1)　h(-1).　The　introduction　of　Ti3C2　MXene　in　g-C3N4　promotes　the　energy　of　photoelectrons　and　the　transport　efficiency　of　photogenerated　carriers　at　the　p-n　heterojunction　interface　via　hot　electron　injection　induced　by　the　localized　surface　plasmonic　resonance　(LSPR)　and　band　structure　regulation.　Meanwhile,　apart　from　the　component　of　p-n　heterojunction,　Cu2O　also　acts　as　the　adsorption　site　of　CO2,　inhibiting　HER　by　blocking　the　adsorption　of　protons.　This　study　provides　a　novel　strategy　to　fabricate　multifunctional　composite　for　efficient　and　highly　selective　CO2　reduction.