Abstract: Because of the limit of energy resources, the fuel used in drying of agricultural products is basically coal in China, especially soft coal. As a result, studying the modern furnace with high thermal efficiency, long service life and heating air without flue gas pollution becomes the key in the developing of drying machines. According to the features of burning of solid fuels and drying of hot air, the authors developed a new model sleeve type highly efficient hot air furnace without flue gas pollution. It is widely used in the drying of grain and other agricultural products. The paper introduces the working principle and the designing method of the furnace and also compares a number of different types of hot air equipments.