The invention belongs to the technical field of the comprehensive utilization of the waste lead slag obtained by the preparation of lithopone in the inorganic chemical industry and particularly relates to a method for preparing iron ingots and co-producing cadmium sulfate and copper sulfate from mixed iron slag through the arc method. The main technical scheme adopted by the invention is as follows: the technology of the arc furnace is adopted to extract heavy metals in the waste residue of lithopone, high-temperature treatment, acid treatment and distillation treatment are performed on the waste residue in turn to obtain iron, copper, cadmium and valuable compounds; and by adopting the invention, the heavy metal waste residue can be completely used and the pollution of heavy metals to the environment can be reduced; and the valuable products can be prepared and the invention has remarkable social benefit and economical benefit.