Will the CO2 capture be affected by the N-doping? This question remains conflict due to the effect of oxygen content in N-doped porous carbons on CO2 uptake has not been systematically investigated. Herein, the effects of N-free and N-doped porous carbons on CO2 uptake were investigated by experiments and theoretical calculations. To elucidate the relative influences of nitrogen functional groups, we synthesized a series of carbons without or with N-doping (2.73-9.44% N) by varying the synthesis conditions. Experimental results show that the introduction of oxygen and nitrogen into carbon framework improves CO2 capture in porous carbons (PCs) and N-doped porous carbons (NPCs). Among these samples, the NPC600 exhibits an exceptionally high CO2 adsorption capacity (5.01 mmol g(-1) at 1 bar and 25 degrees C). Based on the theoretical calculations, the introduction of nitrogen into carbon framework with high oxygen content further enhances electrostatic interaction for CO2 adsorption. Moreover, the doping of nitrogen to carbon framework also has a greater effect on both the selectivity for CO2/N-2 and the isosteric heat of CO2 adsorption. It is predicted that this investigation will eliminate any ambiguities and better explain the influence of N-doping on CO2 capture.