In this study, we found out the relation between Fea3 recovering-concentration and stage number of extraction process for invar (Fe +Ni) etching process. In order to get the desired Fea3 recoveringconcentration economically, we developed the simulation program for designing the optimal Fea3 extraction process. We got the key parameter for this simulation program through pilot scale experiments. The process simulation by the developed program could reduce the emission of waste etching solution as well as the treatment costs. In addition, the developed program could calculate the number of stage of the etchant recovering system and the process time to get the desired concentration of Fea3. This program was used to compute the optimal capacity of the etchant recovering system and applied to the optimization of the stage of the etchant recovering system in real IT industry.