The process adopts the multi effect continuous evaporation mode, using the graphite evaporator as the main equipment and steam as the heat source, the multi effect continuous evaporation is carried out to achieve the purpose of gas liquid separation. The whole system is self circulating in the negative pressure environment. Through practice, it is proved that the waste liquid of acid washing can be treated efficiently, and the by-product of hydrochloric acid and ferrous chloride crystalline salt can be produced, and the comprehensive utilization of resources and zero discharge are realized, and the purpose of harmless treatment is achieved. The by-product hydrochloric acid is reused and the ferrous chloride is used as the raw material for industry. The market is widely used and has certain economic value. Realize the comprehensive utilization of waste and produce value by environmental protection.