The material enters the inner layer of the rotary drum from the feeding device to realize the downstream drying. The material is continuously picked up and scattered under the inner plate in a spiral way to realize the heat exchange. The material moves to the other end of the inner layer and enters the middle layer for countercurrent drying. The material is continuously lifted back and forth in the middle layer in a two-step and one-step way. The material in the middle layer not only fully absorbs the heat emitted by the inner drum, but also absorbs the heat of the middle layer drum, At the same time, the drying time is extended, and the material reaches the best drying state here. The material moves to the other end of the middle layer and falls into the outer layer. The material moves in a rectangular multi-circuit way in the outer drum. The material that has reached the drying effect moves quickly under the action of hot air and is discharged from the drum. The wet material that has not reached the drying effect cannot move quickly because of its own weight. The material is fully dried in this rectangular sheet, thus completing the drying purpose.