The invention discloses a method for processing arsenic in nonferrous metallurgy polluted acid through steel slag treatment. The method includes the steps of putting in steel slag to adjust the pH of nonferrous metallurgy polluted acid, preprocessing the steel slag, putting nonferrous metallurgy polluted acid and preprocessed steel slag in preprocessed polluted acid wastewater according to the volume mass ratio of 100 mL:(1.5-3.0) g to be stirred for 1.5-2 hours at a temperature of 35-50 DEG C, conducting static settlement for 8-10 hours, centrifugally separating supernate, detecting the content of arsenic in filtrate, and entering the next treatment process if the content meets the national standard. The method has the advantages that the raw materials are low in price, steel slag can be easily obtained, water quality adaptability is high, the technological process is short, operation is easy, treatment expenditures are low, actual requirements of enterprises are met, the characteristics of the steel slag are used, other reagents are little added, cost is low, oxidization is not needed, slag amount is small, and stability is achieved; the comprehensive utilization of the steel slag and the purification treatment of nonferrous metallurgy polluted acid are achieved.