Display omitted •Hierarchical N-doped porous carbon was prepared from shells of three crustaceans.•C-GSS-800-1:1 afforded the SSA (1734.64 m2/g) and total pore volume (1.48 cm3/g).•C-GSS-800-1:1 exposed a hierarchical structure with mesoporous proportion (82.43%).•C-GSS-800-1:1 exhibited high CO2 uptake (4.325 mmol/g) and CO2/N2 selectivity (32.32).•Pyrrole N and hierarchical pore structure improved the CO2 adsorption properties. The improved CO2 adsorption capacity and selectivity is the focus of research on the carbon-based CO2 adsorbent, while nitrogen-containing groups on the surface of adsorbent have an important effect on the CO2 adsorption. In this study, nitrogen self-doped hierarchical porous carbon was prepared from three kinds of crustacean shells, namely, hairy crab shell, crayfish shell and greasyback shrimp shell. It revealed that the pore structure of porous carbon can be regulated well with the varied activation temperature and the amount of KOH. With the favorable activation temperature of 800℃ and the mass ratio of activator to carbon (A/C) of 1:1, the obtained porous carbon with different carbon precursors exhibited relatively high specific surface area (1430.63–1734.64 m2/g), large pore volume (0.70–1.48 cm3/g) and developed pore-size distribution. Consequently, among the three kinds of hierarchical porous carbon tested, that prepared form greasyback shrimp displayed the excellent CO2 adsorption of 5.144 and 4.325 mmol/g at 1 bar, 273 K and 298 K and the highest CO2/N2 selectivity was observed of 32.32, attributed to the volume of mesopore and micropore and the type of nitrogen-containing groups. The effects of nitrogen-containing groups in porous carbon on the CO2 adsorption and CO2/N2 selectivity were analyzed, and it revealed that the CO2/N2 selectivity of porous carbon was positively correlated with pyrrolic N. In conclusion, the porous structures and nitrogen-containing groups of porous carbons both contribute to the CO2 adsorption and selectivity. The porous carbon with well recycling performance in this study presented a practical application prospect.