Activated carbon fibers(ACFs) were prepared from general pitch-based carbon fiber by steam activation and catalytic activation method, respectively. The surface area and pore structure of the resultant ACFs were analyzed by N2 adsorption, and electrochemical performances as electrodes of super capacitors were characterized by galvanostatic, cyclic voltammograms and AC impedance spectrum analysis. The results show that ACFs prepared by both methods have similar BET surface area, while their pore size and distribution are different. Compared with steam activation, catalytic activation results in ACFs with high mesoporosity of 40%. The electrode performances show that the specific capacitances of ACFs prepared by catalytic activation method could be 213 F/g, two times of that of ACFs prepared by steam activation method, and more mesopores are the reason for the good capacitance performance.