The spent caustic oxidation unit of ethylene plant plays an important role in environmental protection. The unsaturated sulfide including Na₂S in the spent caustic solution is mainly saturated by oxidation. Before entering the oxidation section, a stripper is generally designed to remove hydrocarbons such as the polymer of carbonyls and dienes carried in the spent caustic solution. This part of hydrocarbons is easy to polymerize at high temperature and block the stripper, affecting the smooth operation of the plant. After the stripper is blocked, it is often repaired by means of hydraulic cleaning, which produces a large amount of hazardous wastes including the polymer of carbonyls and dienes. The wastes are difficult to treat, the operating environment is harsh and the safety and environmental protection risks are high. By establishing the process of wash oil soaking and circulating cleaning in the stripper, the above-mentioned problems can be effectively solved after the project is put into operation smoothly.