Electrochemically driven carbon dioxide (CO2) conversion is an emerging research field due to the global warming and energy crisis. Carbon monoxide (CO) is one key product during electroreduction of CO2; however, this reduction process suffers from tardy kinetics due to low local concentration of CO2 on a catalyst's surface and low density of active sites. Herein, presented is a combination of experimental and theoretical validation of a Ni porphyrin-based covalent triazine framework (NiPor-CTF) with atomically dispersed NiN4 centers as an efficient electrocatalyst for CO2 reduction reaction (CO2RR). The high density and atomically distributed NiN4 centers are confirmed by aberration-corrected high-angle annular dark field scanning transmission electron microscopy and extended X-ray absorption fine structure. As a result, NiPor-CTF exhibits high selectivity toward CO2RR with a Faradaic efficiency of >90% over the range from -0.6 to -0.9 V for CO conversion and achieves a maximum Faradaic efficiency of 97% at -0.9 V with a high current density of 52.9 mA cm(-2), as well as good long-term stability. Further calculation by the density functional theory method reveals that the kinetic energy barriers decreasing for *CO2 transition to *COOH on NiN4 active sites boosts the performance.