Abstract: Grain drying is a complex and unstable process of heat and mass transfer. There are three kinds of mathematical models for describing the process i. e. the empirical , the semi-empirical and the theoretical models. But all these models can only give the macro-drying process and cannot describe the mass-transfer characteristics. The authors use a new mathematical model to describe the grain drying process and introduce a method of studying the mass diffuse coefficient of grain by means of thermal analyser.