The　capture　and　catalytic　conversion　of　CO2　into　value-added　chemicals　is　a　promising　and　sustainable　approach　to　resolve　the　increasingly　severe　global　warming　and　energy　crisis.　However,　the　catalytic　efficiency　for　CO2　reduction　is　seriously　restricted　by　the　free　energy　changes　of　the　intermediate　reaction.　Herein,　using　density　functional　theory　(DFT),　the　electrocatalytic　CO2　reduction　reaction　(CRR)　was　applied　towards　making　C-1　products　(CO,　HCOOH,　CH3OH,　HCHO,　and　CH4)　on　monolayer　C2N　frameworks　with　M-3　(M　=　Fe,　Co,　Ni,　Cu)　metal　clusters　introduction.　Analyses　of　the　adsorption　configurations　and　electronic　structures　suggested　that　CO2　could　be　chemically　adsorbed　on　Fe-3@C2N,　Co-3@C2N,　Ni-3@C2N　and　Cu-3@C2N.　The　H-2　evolution　reaction　(HER),　as　a　suppression　of　CRR,　was　investigated,　and　results　showed　that　the　CRR　selectivity　of　Fe-3@C2N,　Co-3@C2N,　Ni-3@C2N　and　Cu-3@C2N　is　higher　than　that　of　HER.　The　CRR　reaction　produces　different　C-1　products　in　different　reaction　paths　due　to　proton　transfer　on　Fe-3@C2N,　Co-3@C2N,　Ni-3@C2N　and　Cu-3@C2N.　Free　energy　profiles　demonstrate　that　Cu-3@C2N　and　Co-3@C2N　were　identified　to　be　effective　in　catalyzing　CRR　with　lowered　overpotentials　(0.51　V-0.67　V).