Electrocatalytic　nitrogen　reduction　reaction　(NRR)　is　a　promising　method　for　sustainable　production　of　NH3,　which　provides　an　alternative　to　the　traditional　Haber-Bosch　process.　However,　the　poor　Faraday　efficiency　caused　by　N≡N　triple　bond　activation　and　competitive　hydrogen　evolution　reaction　(HER)　have　seriously　hindered　the　application　of　NRR.　In　this　work,　a　novel　strategy　to　promote　NRR　through　boron-transition-metal　(TM)　hybrid　double-atom　catalysts　(HDACs)　has　been　proposed.　The　excellent　catalytic　activity　of　HDACs　is　attributed　to　a　significant　difference　of　valence　electron　distribution　between　boron　and　TMs,　which　could　better　activate　N≡N　bonds　and　promote　the　conversion　of　NH2　to　NH3　compared　with　boron　or　metal　single-atom　catalysts　and　traditional　double-atom　catalysts　(DACs).　Hence,　by　means　of　DFT　computations,　the　stability,　activity,　and　selectivity　of　29　HDACs　are　systematically　investigated　to　evaluate　their　catalytic　performance.　B-Ti@g-CN　and　B-Ta@g-CN　are　screened　as　excellent　nitrogen-fixing　catalysts　with　particularly　low　limiting　potentials　of　0.13　and　0.11　V　for　NRR　and　rather　high　potentials　of　0.54　and　0.82　V　for　HER,　respectively.　This　work　provides　a　new　idea　for　the　rational　design　of　efficient　nitrogen-fixing　catalysts　and　could　also　be　widely　used　in　other　catalytic　reactions.　©　2021　American　Chemical　Society.