The materials drop to the center of millstone through the lay-off tube, and the millstone, which is rotating at constant speed, scatters evenly the material to the outside by means of centrifugal force, making it form material bed with certain thickness. Meanwhile, the material is rolled and smashed by multiple rollers. The material gradually move to the fringe of the millstone under the continuous force of centrifugal force, when the leaving material meets the hot gas entering into the mill through vane and moves upward, entering the separator through the central casing of mill, the material and hot gas achieve sufficient heat exchange and moisture is evaporated quickly in the process. Powder concentrator controls the granularity of finished product at the exit of roller mill, granules that are larger than regulated size are separated and fall to the millstone, while those materials satisfying the fineness requirement enter the finished product storehouse through powder concentrator.