The electrochemical nitrogen reduction reaction (NRR) is currently the most attractive method for ammonia production, in which the development of high efficiency and low-cost electrocatalysts is still a challenge. A lot of recent research has been focused on B single-atom catalysts. However, doping carbon materials with multiple hetero-elements has been rarely explored. Herein, we investigate the catalytic performance of B doped, N doped, and BN co-doped defective graphdiyne (B@GDY, N@GDY and BN@GDY) for nitrogen reduction by using density functional theory. Our results reveal that BN@GDY exhibits higher catalytic efficiency relative to that of single B doping, which is manifested by a significant decrease in overpotential (0.32 V vs. 0.61 V) via the enzymatic mechanism. The projected density of states and Bader charge analysis indicate that BN@GDY can promote the charge transfer from the catalytic substrate to adsorbed N₂, in which the addition of N can convert B from sp² to sp³ hybridization. Meanwhile, the competing hydrogen evolution reaction (HER) can be well inhibited during the NRR for both B/BN@GDY substrates, especially in BN@GDY, indicating the high selectivity of BN@GDY towards the NRR. Above all, this work puts forward a novel metal-free electrocatalyst for the NRR and may provide useful guidance for the design of new non-metal nitrogen reduction electrocatalysts.