N-doped porous carbons (NPCs) are characterized by well-developed porosity and N-doped active sites, which makes them suitable for CO2 capture. However, their application in practice is obstructed by the relatively low N-doped content and unsatisfactory adsorption capacity. Herein, we report the synthesis of NPCs through the rational design of the precursor NUT-21 (NUT means Nanjing Tech University) with a record-high N content (up to 46.16%, wt). The NUT-21 was fabricated by the polymerization of two simple monomers of 2,4,6-tris(bro-momethyl) mesitylene and 3,5-diamino-1,2,4-triazole with an unusually high N content of 70.67% (wt). With the carbonization of NUT-21 at different temperatures (500, 600, and 700 degrees C, respectively), a series of NPCs possessing various porosity and N contents are produced, successfully. For the NPC generated at 600 degrees C, the N content can reach 7.41% (wt), the surface area is 2208 m(2)/g, the micropore volume is 0.791 cm(3)/g, and the CO2 capacity is up to 8.3 mmol/g at 273 K and 1 bar, which is much higher than those of benchmarks including 13X zeolite (4.1 mmol/g) and activated carbon (2.8 mmol/g), and most carbon-based adsorbents reported till now. It was proved in our previous studies that the ultrahigh N content of the precursor was beneficial for both the formation of developed porosity and the generation of abundant N-doped sites, which can give rise to superior capacity and selectivity of CO2 capture. The NPCs obtained may offer to be highly promising candidates for CO2 separation from gas mixtures including natural gas and flue gas.