Hydrodynamic cavitation (HC) and Fe(II) are advanced oxidation processes, in which pentachlorophenol (PCP) is treated by the redox method of activating persulfate (PS). The kinetics and mechanism of the HC and Fe(II) activation of PS were examined in aqueous solution using an electron spin resonance (ESR) spin trapping technique and radical trapping with pure compounds. The optimum ratio of Fe(II)/PS was 1:2, and the hydroxyl radical (HO) and sulfate radical (SO) generation rate were 5.56 mM h and 8.62 μM h, respectively. The generation rate and R of HO and SO at pH 3 and 50 °C in the Fe(II)/PS/HC system are 7584.6 μM h, 0.013 and 24.02 μM h, 3.95, respectively. The number of radicals was reduced as the pH increased, and it increased with increasing temperature. The PCP reaction rate constants was 4.39 × 10 min at pH 3 and 50 °C. The activation energy was 10.68 kJ mol. In addition, the mechanism of PCP treatment in the Fe(II)/PS/HC system was a redox reaction, and the HO/SO contribution was 81.1 and 18.9%, respectively. In this study, we first examined PCP oxidation through HO and SO quantification using only the Fe(II)/PS/HC process. Furthermore, the results provide the foundation for activation of PS by HC and Fe(II), but also provide a data basis for similar organic treatments other than PCP.