Although single-atom catalysts (SACs) have been widely employed in the CO2 reduction reaction (CO2RR), the understanding regarding the effect of morphological attributes on catalytic performance are still lacking, which prevents the rational design of high-performance catalysts for electrochemical CO2RR. Here, we developed a novel catalyst with axial Co-N5 sites embedded on controllable mesoporous carbon nanosphere with different graded pore structures. Benefiting from the precise control of porosity, the influence of morphological attributes on catalytic performance was well revealed. In situ characterization combined with density functional theory (DFT) calculations revealed that axial N-coordination induced local d-p orbitals coupling enhancement of Co with oxides and the optimal pore size of 27 nm promoted the interfacial bonding characteristics, which facilitate both the COOH* generation and CO desorption. Consequently, A superior selectivity of nearly 100% at -0.8 V vs. RHE and commercially relevant current densities of >150 mA cm−2 could be achieved, and a strikingly high turnover frequency of 1.136*104 h−1 at -1.0 V has been obtained, superior to the most of Co-based catalysts.