Carbon capture has emerged as an efficient technology for mitigating escalating atmospheric CO2 levels. Porous carbons show the promising potential for CO2 capture by virtue of their tunable porosity and surface chemistry, while typically exhibit limited capacity owing to the trade-off between high porosity and surface functionalization. Herein, we develop an innovative dynamic activation strategy with CuCl2 as porogen to construct biomass-derived hierarchical porous carbons (HPC) with gradient porosity. This method not only enables precise tailoring of pore size and surface heteroatom doping to synchronously achieve a high porosity and surface groups, but also allows the recycling of porogen, aligning with green and sustainable chemistry principles. The optimized HPC material exhibits ultrahigh specific surface area (up to 2856.9 m2 g-1), well-interconnected micropores and satisfactory surface functional groups. Systematic investigations reveal that ultramicropores (<0.7 nm) dominate CO2 adsorption at low pressure, while larger micropores and mesopores contribute more for capacity at high pressure. The optimal sample achieves superior CO2 uptakes of 6.95, 4.32, and 2.07 mmol g⁻¹ at 273, 298, and 323 K under 1 bar, respectively, alongside high CO2/N2 selectivity (up to 91 at 298 K). Furthermore, pyridinic-N and pyrrolic-N groups significantly improve selectivity, and meanwhile the HPC materials demonstrate rapid adsorption kinetics and excellent cyclic stability. This work not only advances the fundamental understanding of dynamic activation mechanisms, but also establishes a sustainable pathway for designing porous carbon adsorbents for high-effective CO2 capture.