The invention provides a limonite treating method combining atmospheric-pressure acid leaching and medium-pressure leaching, is aimed at providing of a hydrometallurgical process that is low in acid consumption and high in leaching rate for limonite, and relates to a process method for subjecting high-silicon high-magnesium ore of the limonite to sulfuric acid atmospheric-pressure leaching and subjecting low-silicon low-magnesium high-iron ore to pressure leaching by utilization of atmospheric-pressure leachate in the same process. The method achieves efficient development and utilization of the limonite, adopts the process combining the atmospheric-pressure acid leaching and the medium-pressure leaching, overcomes the defects that present high-pressure acid leaching processes need autoclaves and related devices so that the manufacturing and maintenance costs are high, and overcomes the technical problem that the high-pressure acid leaching processes are high in acid consumption and are limited to treatment of limonite type raw materials. Compared with atmospheric-pressure leaching processes, the method has beneficial effects comprising higher nickel and cobalt recovery rates, easy and effective separation of leached slag, and the like.