In view of the problems of high energy consumption and serious secondary pollution during traditional electric regeneration of activated carbon, cathodic electric field was adopted to activate persulfate in situ for regenerating phenol saturated activated carbon fiber (ACF), and the regeneration efficiency of ACF and degradation efficiency of pollutants in the regeneration solution were investigated. The adsorption process of ACF was fitted by Langmuir and Freundlich adsorption isotherm models. The effects of current density, persulfate concentration, and regeneration time on the electric cathode/persulfate regeneration process were investigated. Besides, the application potential and regeneration mechanism were analyzed by multiple adsorption–regeneration cycles experiments. Results show that the adsorption of phenol by ACF was more consistent with the Freundlich adsorption isotherm model, indicating heterogeneous adsorption. The regeneration efficiency of the electric cathode/persulfate regeneration process was 62.71%, and the total amount of phenol in the regeneration solution was only 3.10% of the maximum adsorption capacity of ACF. The optimal operating conditions were current density of 57.14 mA/cm², persulfate concentration of 0.1 mol/L, and regeneration time of 6 h. During the multiple regeneration of the electric cathode/persulfate process, the persulfate and the resulting sulfate radical would damage the pore structure and surface morphology of ACF to some extent. After three times of regeneration, the regeneration efficiency could still reach about 40%, which indicates that the process has strong application potential.