Electrochemical reduction of dinitrogen molecules (N ) to value-added ammonia by using renewable electricity under mild conditions is regarded as a sustainable and promising strategy for N fixation. However, the lack of efficient, robust and inexpensive electrocatalysts for such electrochemical reduction has prevented its wide application. Herein, we report a novel single-atom catalyst, i.e., a single tungsten (W) atom anchored on N-doped graphyne (W@N-doped graphyne) as a highly efficient and low-cost electrocatalyst for the N reduction reaction. The inert Ntriple bond, length as m-dashN triple bond can be sufficiently activated when an N molecule is adsorbed on the W atom. A single atom of W coordinated with one N atom (doping into an sp-hybridized carbon atom) exhibits the highest catalytic performance with ultra-low onset potential of 0.29 V for N reduction reactions. The 'distal mechanism' is identified as the most favourable catalytic pathway. Moreover, the improved electrical conductivity of W@N-doped graphyne compared to that of pristine graphyne can ensure better electron transfer efficiency during the reduction processes. Our study provides a novel electrocatalyst with excellent catalytic performance for electrochemical reduction of N to NH under ambient conditions.