A new method of alkali solution analysis was established, which could accurately analyze the NaHCO₃ and NaHS content of waste alkali liquor to provide adjustment basis for the transformation of caustic wash system from Lummus caustic wash process to Nagao soda caustic wash process. By adding caustic injection line to the caustic wash system, the injection amount of fresh alkali liquor can be timely adjusted when the sulfur content fluctuates, thus effectively reducing the usage of fresh alkali liquor and avoiding the unqualified caustic wash. By adding water injection line to the caustic wash system, the plugging of pipeline caused by the crystallization of waste alkali liquor delivered can be prevented. By reducing the formation of grease in the caustic wash system and maintaining proper caustic wash temperature and pressure, the stable operation of the caustic wash system can be ensured. After the optimization and adjustment of the caustic wash system, the concentration of the first-stage alkali liquor decreased from 1％~2％ to 0, and the concentration of the second-stage alkali liquor decreased from 8％~15％ to 8％~10％. The fresh alkali consumption per ton of ethylene was reduced from 6.3 kg to 3.6 kg, and the waste alkali discharge per ton of ethylene was reduced from 21.4 kg to 16.3 kg, achieving the emission reduction of caustic wash system.