Electrocatalytic　nitrogen　reduction　reaction　(NRR)　is　one　of　the　most　promising　approaches　to　achieving　green　and　efficient　NH3　production.　However,　the　designs　of　efficient　NRR　catalysts　with　high　activity　and　selectivity　still　are　severely　hampered　by　inherent　linear　scaling　relations　among　the　adsorption　energies　of　NRR　intermediates.　Herein,　the　properties　of　ten　M3B4　type　MBenes　have　been　initially　investigated　for　efficient　N2　activation　and　reduction　to　NH3　via　first-principles　calculations.　We　highlight　that　Cr3B4　MBene　possesses　remarkable　NRR　activity　with　a　record-low　limiting　potential　(-0.13　V).　Then,　this　work　proposes　descriptorbased　design　principles　that　can　effectively　evaluate　the　catalytic　activity　of　MBenes,　which　have　been　further　employed　to　design　bimetallic　M2M＇B4　MBenes.　As　a　result,　5　promising　candidates　including　Ti2YB4,　V2YB4,　V2MoB4,　Nb2YB4,　and　Nb2CrB4　with　excellent　NRR　performance　have　been　extracted　from　20　bimetallic　MBenes.　Further　analysis　illuminates　that　constructing　bimetallic　MBenes　can　selectively　tune　the　adsorption　strength　of　NHNH2**　and　NH2NH2**,　and　break　the　linear　scaling　relations　between　their　adsorption　energies,　rendering　them　ideal　for　NRR.　This　work　not　only　pioneers　the　application　of　MBenes　as　efficient　NRR　catalysts　but　also　proposes　rational　design　principles　for　boosting　their　catalytic　performance.