Developing high efficient and cheap electrocatalysts for carbon dioxide reduction reaction (CO2RR) is the key to achieve CO2 transformation into clean energy. Herein, a series of transition metal dimer and nitrogen codoped graphene (M2N6-Cra, M = Cr-Cu) acting as electrocatalysts for CO2RR are investigated based on the density functional method. For M2N6-Cra (M = Cr, Mn), the selectivity is poor and CO poisoning is serious. Fe2N6-Cra is the best CO2RR catalyst due to the good selectivity and catalytic activity. The calculated overpotential is very small, i.e., 0.03 V for COOH channel, 0.05 V for HCOO channel. Hydrogen evolution reaction is also refrained on the Fe2N6-Cra surface, which further supports its high catalytic performance. For M2N6-Cra (M = Co, Ni, Cu), the catalytic activity is poor due to large overpotentials. These results indicate that if designed carefully, the transition metal dimer and nitrogen codoped graphene would be good candidate for the high efficient and selective CO2RR catalyst. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.