In　this　study,　we　designed　a　series　of　Fe-doped　C3BN2　electrocatalysts　through　vacancy　engineering,　including　FeBv,　Fe-Nv,　Fe-Cv,　Fe-Bv-Cv,　and　Fe-Cv-Nv,　to　enhance　catalytic　activity　for　electrocatalytic　nitrogen　reduction　reaction　(NRR)　toward　ammonia　synthesis.　Using　density　functional　theory　(DFT)　simulations,　we　investigated　nitrogen　adsorption　and　Gibbs　free　energy　changes　during　the　key　hydrogenation　steps,　identifying　the　first　hydrogenation　step　(*N2　-＞*N2H)　as　a　potential-determining　step　(PDS).　Among　the　catalysts,　Fe　anchored　at　Cvacancy-defected　C3BN2　(Fe-Cv)　exhibited　the　best　nitrogen　reduction　reaction　(NRR)　performance　with　a　low　Gibbs　free　energy　barrier　(Delta　G　=　0.60　eV)　and　a　low　overpotential　of　0.44　V,　favoring　distal　and　alternating　reaction　pathways.　The　superior　catalytic　activity　of　Fe-Cv　is　attributed　to　strong　N2　chemisorption　(Delta　G　=-1.33　eV)　and　effective　activation　of　the　N　equivalent　to　N　bond　via　Fe　3d　electron　back-donation.　Additionally,　Fe-Cv　shows　high　selectivity　for　NRR　over　hydrogen　evolution　reaction　(HER)　and　excellent　thermal　stability　up　to　500　K.　These　findings　suggest　that　Fe-Cv　is　a　promising　catalyst　for　efficient　ammonia　synthesis　and　provide　valuable　insights　into　the　design　of　single-atom　NRR　electrocatalysts.