Abstract: The degradation of phenol in water was systematically investigated with the oxidation of H₂O₂ enhanced by hydrodynamic cavitation.The effects of inlet pressure,the mass concentration of H₂O₂ and the presence of dissolved gases were discussed in detail.The difference of the energy efficiency between hydrodynamic cavitation and acoustic cavitation was also discussed.The experimental results show: the rate of phenol degradation increases from 17.6% to 47.6% with increasing inlet pressure from 1.0×10⁵ to 3.5×10⁵ Pa correspondingly;under certain conditions,the mass concentration of added H₂O₂ has an optimum value;different dissolved gases have different influence on the degradation effect of phenol,and O₂ is more efficient than N₂.By analyzing the influence of H₂O₂ mass concentration and dissolved gases on the degradation of phenol,and investigating the concentration distribution of the intermediate products,it can be concluded that the formation of ·OH free radicals is the main reason of the degradation of phenol.Degradation of phenol per unit energy input for hydrodynamic cavitation is 5.4 times higher than that for acoustic cavitation.