Porous activated carbon fiber (ACV) is prepared from oxidized polyacrylenitrile (PAN) fiber through three activation methods, which are traditional chemical activation, traditional physical activation, and ameliorative chemical activation. The samples under various high temperature heat treatments are used as electrode for the supercapacitor. The structure and electrochemical properties of these samples are than characterized by nitrogen adsorption at 77 K, X-ray diffraction (XRD), Raman spectrum, electron spectroscopy for chemical analysis (ECSA), Fourier transform infrared spectrometer (FTIR), cyclic voltammetry (CV), and glavanotactic charge/discharge, respectively. Once formed by the ameliorative chemical activation method, which is used for the electrodes of supercapacitors, the sample exhibited excellent capacitance characteristics in the 1 M H2SO4 electrolyte and a high discharge capacitance of 180 F/g Moreover, HP20-1/3-900 has near triangular shapes, reflecting their excellent charge/discharge capaeitive performance. Results of this study demonstrate that the ameliorative activation process for preparing makes this activated carbon fiber a highly promising electrode material for industrial applications of supercapacitors.