Ammonia　is　an　important　industrial　raw　material.　To　promote　the　production　of　ammonia,　it　is　urgent　to　develop　efficient　catalysts　for　nitrogen　reduction　reactions　(NRR).　Here,　we　have　reported　a　novel　electrocatalyst:　γ-graphyne-like　BN　sheet-supported　single　metal　atom　(M/γBN,　M　=　Sc,　Ti,　V,　Cr,　Mn,　Fe,　Co,　Ni,　Cu,　Zn,　and　Ru)　for　NRR　and　studied　the　effect　of　Hubbard　U　correction　in　single-atom　catalysts.　The　results　of　adsorption　show　that　Ti/γBN,　V/γBN,　and　Ru/γBN　have　the　best　adsorption　energy　for　nitrogen.　A　detailed　analysis　of　the　NRR　mechanism　indicates　that　V/γBN　has　the　lowest　energy　barrier　in　the　rate-determining　step　when　it　follows　a　distal　mechanism.　Further　analysis　shows　that　the　superior　catalytic　performance　in　V/γBN　sheet　is　mainly　attributed　to　the　electron　donation　and　back-donation　mechanism.　More　interestingly,　V/γBN　greatly　inhibited　HER　selectivity.　By　analyzing　the　doping　structure　and　adsorption　system,　it　can　be　found　that　when　considering　Hubbard　U　correction,　there　will　be　an　obvious　correlation　between　energy　and　distance.　This　study　not　only　provides　a　basis　for　understanding　the　mechanism　of　nitrogen　reduction　reaction　catalyzed　by　single-atom　catalysts　but　also　provides　a　new　design　idea　for　the　rational　design　of　high-efficiency　NRR　catalysts.　©　2022　Elsevier　B.V.