A facile and environmentally friendly approach to produce self-doped hierarchically porous carbon as electrode material for high-performance supercapacitor was demonstrated. Three-dimensional honeycomb-like hierarchically porous carbon was successfully obtained by one-step carbonization and activation of sodium carboxymethyl cellulose (CMC) via K2CO3. With the optimized temperature of carbonization and activation, the porous carbon material achieved well-shaped hierarchically pores (micro-, meso-, and macropores) like a honeycomb, ultrahigh specific surface area (1666 m2 g−1), as well as highly O-self-doping (3.6 at%), endowing an excellent electrochemical properties for the electrode in a three-electrode system. The porous carbon electrode material delivered a high specific capacitance of 300.8 F g−1 at 1 A g−1, an eminent rate capability of 228.4 F g−1 at the current density up to 20 A g−1 and outstanding cycle stability of 94.3% retention after 10,000 cycles. Therefore, the CMC-derived hierarchical porous carbon activated by K2CO3 would have promising foreground in the application of supercapacitors.