The spent caustic in ethylene plant has high concentrations of COD and sulfide and is difficult to be treated. This paper introduces the application of wet oxidation technology for spent caustic in ethylene plant, summarizes the actual operation and the problems emerged, analyzes the problems, and puts forward some corresponding solutions to optimize the operation of the plant. After modification, the spent caustic with high COD and high sulfide produced by ethylene plant is treated as high salt wastewater with low COD and low sulfide.