Abstract It is extraordinarily valuable to develop the supercapacitor with high capacitance retention under ultra-high current density to meet the requirement of fast charging. Herein, porous carbons with tailored graphitization degree and pore size distribution are facilely prepared via controlling the activation temperature of biomass-derived pyrolytic carbon when employing potassium ferrate (K2FeO4) as catalyst and activation agent. The obtained semi-graphitized microporous carbon with a large specific surface area (2208 m2 g−1), high proportion of large micropores (more than 71.8%) and high conductivity (2.38 S cm−1) exhibits a perfect balance between the charge storage capacity and rate capability, which specific capacitance reaches 254 and 273 F g−1 at a current density of 0.5 A g−1 in KOH and H2SO4 aqueous electrolyte, respectively. Surprising capacitance retention of 86.9% is obtained under an ultra-large current density of 100 A g−1 for the symmetrical supercapacitor based on the semi-graphitized microporous carbon, and no apparent attenuation was observed after 10,000 cycles. Furthermore, energy density of the assembled symmetrical supercapacitor reaches 7.4 Wh kg−1 at a power density of 151.4 W kg−1, and more than 87.8% of energy density is kept even under an ultra-large power density of 29.1 kW kg−1.