Single-atom catalysts with ultra-high atomic utilization and selectivity show great potential in the production of NH₃ through electrocatalytic nitrogen reduction reaction (NRR). In this paper, 13 single-atom cadmium sulfide (TM − CdS) doped with different transition metals (TM) (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Ag) were constructed separately using a density functional theory approach to calculate the structural stability and the reaction mechanism of catalytic ammonia synthesis. hree systems, Fe − CdS, Mo − CdS, and Ru − CdS, were screened out from the 13 doped metal 0structures on the basis of the computational results. The above three systems have more stable structures, can transfer more charge to activate N₂ molecules, and exhibit better NRR catalytic activity. The limiting potential NRR on the Mo − CdS structure is only − 0.261 V, which is lower than that of Fe − CdS (−0.353 V), Ru − CdS (−0.461 V) and CdS (−2.124 V). This work will be of great value of designing and employing the doped single-atom catalysts for efficient electrolytic nitrogen reduction reaction.