According to the characteristics of plant impurities and dust and other waste gas, combined with the characteristics of the grain dryer, the fully closed structure and the centralized separation and recovery process of dust and impurities by negative pressure were used to change the open drying operation mode and achieve the orderly discharge of plant impurities and dust. Through the production verification, 90% of plant impurities and dust can be recoveried, and more than 3% of source of energy can be saved. It can not only solve the environmental pollution problems such as excessive emission of exhaust gas, but also can turn waste into wealth during recycling waste processing into biomass particles. Moreover, the heat loss of dryer can be reduced, and the drying thermal efficiency can be improved.