Aqueous oxidation of phenanthrene and pyrene which are the representatives of three-and four-ring polycyclic aromatic hydrocarbons with Fenton reagent has been studied.The factors affecting degradation efficiencies of polycyclic aromatic hydrocarbons,such as dosage of Fe2+,dosage of H2O2,pH value,reaction temperature and time have been systematically examined.The optimal operating conditions have been obtained.For a stimulant water sample containing 5.0mg/L phenanthrene and pyrene respectively,when the concentration of Fe2+ was 5.0 mmol/L,the concentration of H2O2 was 20.0 mmol/L、pH value of the solution was 6.5、the reaction temperature was 70℃and the reaction time was 1h,the degradation efficiency of the two compounds could reach 84.56% and 92.47% separately.