The　electrocatalytic　CO2　reduction　reaction　(CO2RR)　represents　an　effective　way　to　address　energy　crises　and　environmental　issues　by　converting　CO2　into　valuable　chemicals.　Single-atom　catalysts　(SACs)　can　achieve　excellent　catalytic　activity　in　CO2RR.　However,　the　study　of　CO2RR　on　SACs　still　poses　significant　challenges,　especially　in　terms　of　controlling　the　selectivity　towards　the　deep　product　such　as　CH4　and　CH3OH.　Herein,　we　employ　density　functional　theory　(DFT)　calculations　to　investigate　the　CO2RR　on　Cu　SAC　supported　on　N-doped　graphene　(Cu-N/C)　and　explore　the　role　of　N　dopants　on　the　CO2RR　performance.　Compared　to　Cu　SACs　supported　on　N-doped　defective　graphene　with　double　vacancy　(Cu-N/C-DV),　Cu　SACs　supported　on　N-doped　defective　graphene　with　single　vacancy　(Cu-N/C-SV)　can　effectively　convert　CO2　into　the　deeply　reduced　C-1　products,　including　CH4　and　CH3OH,　thus　further　indicating　that　Cu-N/C-SV　has　a　stronger　interaction　with　&　lowast;CO,　which　is　conducive　to　the　deep　reduction　of　&　lowast;CO.　Increasing　the　coordination　number　of　N　atoms　or　the　proximity　of　doping　site　to　the　Cu　active　site　can　effectively　enhance　the　stability　of　catalyst　and　promote　the　adsorption　of　&　lowast;CO　on　Cu-N/C-SV.　However,　this　also　increases　the　free　energy　of　the　formation　of　&　lowast;CHO　intermediate.　The　results　suggest　that　CuC3-N-m,　which　contains　a　N　atom　in　the　second　coordination　shell　(meta-position)　of　Cu　SACs,　has　the　best　electrocatalytic　performance　of　CO2RR　in　terms　of　both　selectivity　and　catalytic　activity,　not　only　contributing　to　an　in-depth　understanding　of　the　reaction　mechanism　of　CO2RR　on　SACs　but　also　providing　insights　into　the　design　of　SACs　for　efficient　CO2RR.