Abstract: The electrocatalytic nitrogen reduction reaction (NRR) can transform nitrogen and protons from aqueous electrolytes to ammonia by using renewable electricity under ambient conditions, which is a promising technology to replace the Haber-Bosch process. However, this technology is extremely challenging as it requires highly active electrocatalysts to break the stable triple-bonds of N₂.With p bands,main-group s-block metals have been rarely explored in NRR compared with transition metals.Herein, we employ first-principles calculations to propose a Mg single atom catalyst as a promising high-performance electrocatalyst for NRR, where Mg atom is coordinated with four oxygen atoms within graphene (Mg-O₄). Our results reveal that N₂ can be efficiently activated on Mg-O₄ and reduced into NH₃ through the alternating mechanism. Moreover, ab initio molecular dynamics simulations demonstrate the Mg-O₄ structure has high stability.