We studied experiments on phenol wastewater treated by hydrogen peroxide assisted with a cavitating water jet. Removal efficiency factors were studied, and the intermediate products analyzed by High performance liquid chromatography (HPLC) to reveal the degradation mechanism. The optimal cavitating condition was obtained via experimentation. Based on the results, the removal ratio of phenol reaches 99.85% under when the initial phenol concentration is 100 mg/L, the pH value is 3.0, the hydrogen peroxide concentration is 300 mg/L, the confining pressure is 0.5 MPa, and the jetting pressure is 20 MPa. The HPLC analysis shows that the ultimate products of oxidized phenol are maleic acid and acetic acid with the intermediate products of catechol, hydroquinone and pbenzoquinone.