China is facing the significant pressure of environmental protection; Advanced Oxidation Technology (AOT) is an ideal green technology that could well solve the problem involving environmental pollution. AOT refers to the preparation of hydroxyl (·OH) radicals, inducing a series of reactions with ·OH radicals that attacks pollutants and microorganism, therefore AOP is able to thoroughly solve the re-pollution problem in the process of pollution treatment at the source. Since the producing ·OH radicals with a large scale is a key technology in the study of AOT, many scholars have done a series of studies on the ·OH radicals preparation. The major methods of producing ·OH radicals in water, including O₃/H₂O₂, O₃/UV, H₂O₂/UV, Fenton, photocatalytic oxidation, electronic radiation, and water excited, are introduced. The methods of producing ·OH radicals method by air discharge, such as pulse corona, electron beam, and strong ionization discharge are also presented. The strong ionization discharge method could solve the problem producing ·OH radicals with large scale in the water or in the gas.