The gentle electrocatalytic conversion of carbon dioxide into high value-added chemicals electrocatalysis can alleviate the greenhouse effect and energy crisis. Dual-atom catalysts exhibit high atom utilization, and can change their adsorption configuration through double sites to reduce the reaction energy barrier and optimize the reaction path. In this study, the density functional theory calculations were performed to better understand the good performance of NiSn dual-atom catalysts in the reduction of carbon dioxide to HCOOH. The NiSn dual-atom in DM1 model exhibited good stability, activity, and selectivity, which may be the origin of the excellent performance of the NiSn dual-atom catalysts in HCOOH production. The present work provides new ideas for the design of catalysts for the CO2 reduction reaction.