A series of highly porous nitrogen doped porous carbons (NPCs) have been successfully prepared using a novel porous polyimine as the precursor. The resulting NPCs have a high specific surface area of up to 3195 m² g^-1, high pore volume and micropore volume (up to 1.58 and 1.38 cm³ g^-1, respectively), narrow micropore size distributions, and adjustable nitrogen (1.52-5.05 wt%) depending on the activation temperatures (600-750 °C). The CO₂ uptakes of the NPCs prepared at higher temperatures (700-750 °C) are lower than those prepared at milder conditions (600-650 °C). At 1 bar, NPC-650 demonstrates the best CO₂ capture performance and could efficiently adsorb CO₂ molecules of 3.10 mmol g^-1 (136 mg g^-1) and 5.26 mmol g^-1 (231.3 mg g^-1), at 25 and 0 °C, respectively. The NPCs also show good a initial CO₂/N₂ adsorption selectivity of up to 23.4 and an adsorption ratio of CO₂/N ₂ (6.6) at 1 bar. Meanwhile, these NPCs exhibit a high stability and facile regeneration/recyclability without evident loss of the CO₂ capture capacities.