The activated carbon paper (ACP) has been designed as the active electrode material of supercapacitor to improve its capacitive performance. ACP is prepared by electrochemical nitrate ion–assisted exfoliation, sulfate ion–assisted exfoliation, and subsequent hydrothermal reduction processes. The as-prepared ACP shows obviously rougher surface along with the expanded layer distance. ACP exhibits higher specific capacitance of 380 mF/cm2 at 1 mA/cm2 than that of 21 mF/cm2 for carbon paper. ACP electrode shows the cycling capacitance retention of 98% after 5000 cycles at 10 mA/cm2. The symmetric ACP supercapacitor is constructed using ACP electrode and H2SO4 involved polyvinyl alcohol gel electrolyte. ACP supercapacitor presents the specific capacitance of 97 mF/cm2, the energy density of 0.343 mW h/cm3, and the output voltage of 1.6 V at 1 mA/cm2. ACP with high capacitance performance presents the promising supercapacitor application for the electrochemical energy storage.