Abstract: The spherical structure can reduce the transmission distance of electrode ions. Preparation the porous carbon spheres with spherical structure, high specific surface area and simple method is critical for the electricity storage device. In this paper, the porous carbon spheres were obtained from waste liquid via hydrothermal treatment followed with K₂FeO₄ activation. The effect of K₂FeO₄ mass on the capacitive behavior of porous carbon spheres was investigated in detail. The results show that the samples obtained display spherical structure with hierarchical pore size distribution, which contain rich micropores and some mesopores. In the three system, the sample (PCS-2) with the mass ratio of K₂FeO₄ to char of 2 possesses high specific surface area and good electrochemical performance. In addition, the specific capacitance of PCS-2 is as high as 323 F/g at the current density of 0.5 A/g in 6 mol/L KOH electrolyte. The symmetric supercapacitor assembled with K₂FeO₄ to char of 3 electrode can deliver 47.2 W·h/kg energy density and maintain 89% capacitance after 10000 cycles in 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid.