Commercial carbon fiber cloth (CFC) is treated by the Joule-heating pyrolysis method in air to boost its capacitive performance on the premise of energy- and time-saving considerations. A thermoelectric coupling model suitable for the Jouleheating pyrolysis is successfully established based on the comparisons between the simulated temperatures and actually measured ones. The temperature field on CFC surface induced by the Joule heat presents a concentric-ellipse shape that the temperature in the core is the maximal and gradually decays outward. Increasing the direct current (DC) voltage which is applied to the CFC from 1.0 to 6.0 V, the core temperature on the CFC surface can be raised from 31 to 519 °C. The specific surface area and hydrophilicity of the as-prepared porous CFC are greatly improved compared with the pristine one. Electrochemical test shows that the optimal Joule-heating pyrolysis parameters falls at 5.0 V and 12.5 min, and the areal specific capacitance of as-obtained CFC-5.0-12.5 is about 80 folds that of the pristine CFC. In addition to the much shorter preparation time, all the characteristics including areal specific capacitance, rate performance, and electrical conductivity of the Joule-heating pyrolyzed CFC are superior to those of the electrical furnace pyrolyzed counterpart. The aqueous symmetrical supercapacitor made of CFC-5.0-12.5 electrodes exhibits considerable power and energy densities with respect to the previously reported carbon electrode-based supercapacitors. For conductive precursors, the Joule-heating pyrolysis can be an ideal substitute for the traditional electric furnace pyrolysis.