Abstract: The marmatite with high indium and iron contents pressure acid leaching process was simulated with pyrite and indium sulfate, the initial acid concentration, temperature, time, pressure and other factors affecting the leaching were investigated, the conclusions drawn are that the indium will go into the slag residues together with the jarosite, iron hydroxide colloid, and hematite generation, in which the crystalline hematite is better, indium absorbed by the slag is minimum. In order to make the indium absorbed by the slag as little as possible, the precipitation of iron should be reduced, and the precipitation of iron preferably presents in the form of hematite.