Abstract: Abstract: The traditional drying theory of grain materials is mainly based on the assumption of moisture transfer in continuous medium at present, which indicates that the difference between the skeleton and pore is ignored. However, the complex structure inside grain stack is closer to a discrete solid, and the internal part of grain is a multi-layer physical structure, including seed coat (hull), chaff and embryo tissue. Obviously, it is not consistent with the actual situation to ignore the influence of these factors on drying process. So, in order to study the mechanism of heat and mass transfer for the grain drying in bin and the effect of rice stack structure characteristics on the drying process, the basic idea of multi-scale theory was introduced to the drying research field of grain materials in this paper, and a multi-scale and multi-layer structural model of heat and mass transfer processes for grain drying was established by applying the pore network method and taking the rice in bin as the study object, of which the physical model included the pore-throat-pore network and the skeleton (grain) and the rice stack was divided into the particle scale and the dryer scale. The difference of skeleton and pore at different scale was taken into account by distinguishing the mechanism of heat and mass transfer at different scale, and the corresponding heat and mass transfer theory was applied to describe the heat and mass transfer process during the drying in rice stack porous media. The information correlation point between the 2 adjacent scales was found to fuse the corresponding heat and mass transfer information. The effect of rice stack structure characteristics on the drying process was considered by obtaining the rule of the rice packing structure transformed into the pore network and coupling the momentum, energy and mass equations. An experimental study on rice drying was conducted in order to validate this model. The drying bed of experiment was a rectangular cavity with 0.1 m thickness, 0.2 m width and 0.2 m height. There was an air inlet with the shape of isosceles right triangles at the bottom of the drying container, the top of the drying container was as air outlet open to the atmosphere, and there were 14 holes opened on the front wall of the drying container, which were for measurements of the air humidity and temperature. The simulation and experimental results indicated that the established model could explain the mechanical properties of rice drying well. The maximum relative error between the simulation results and experimental data for the average moisture content of rice stack in the container was about 7.6%, and the maximum relative error between the simulation results and experimental data for the dry basis moisture content of single grain of rice at air inlet was approximately 6.8%. During the drying process, the temperature of rice was about 2 K lower compared with the corresponding vapor temperature, and the traditional drying theory that neglected the difference between the grain skeleton and pore was inappropriate. The heat transfer rate of rice grain was much faster than the mass transfer rate and there was a higher moisture gradient inside the rice particle. The diffusion coefficient of rice embryo played an important role in the drying process, whose effect on drying was larger than that of rice hull and chaff. The migration of the moisture in the rice grain from embryo to hull surface became much more difficult when the diffusion coefficient of rice embryo was very small, and the moisture was imprisoned effectively inside the rice grain. The research results can provide a theoretical basis for the design of the process and equipment of the grain drying in bin.