The raw materials to be treated should distribute on the conveyer belt through suitable mechanism such as star distributor, swing belt, crusher or granulator, the conveyer passes through the channel including of one or several heating unit. Each heating unit is equipped with air heater and circle system. Each channel has one or several damp discharge systems. When the conveyer passes through it, hot air will pass through the raw material from up to low or from low to up. In this way raw materials can be dried evenly.