In the plastics processing industry, products show signs of shrinkage, silver streaks, bubbles, cracks, flow marks, and poor transparency. The main reasons for these poor qualities are the failure to fully dry the plastic before forming it. Engineering plastics such as : PA, PET, PC, PBT, CA and other hygroscopic raw materials, because the moisture penetrates into the plastic particles, the traditional hot air dryer cannot make it completely dry. It has been proven in practice that reducing the dew point of the drying wind to below -40 ° C and controlling the heat to blow it across the surface of the wet plastic granules can reduce its moisture content to less than 0.02% before molding. In the circulation system, the air is fully dehumidified and heated, and the dry air quickly precipitates the moisture in the plastic pellets completely to achieve the effect of dehumidification and drying.