A pore network model for drying of grain materials was established on the base of pore network theory and transport process principle, and a corn drying experiment was conducted to verify the validity of this model. The experiment and simulation results indicated that this model could explain the drying process of grain materials well. There is a significant difference between the corn and pore vapor temperature, and it is unreasonable to confuse the two kinds of temperature. The particle size distribution has a great effect on the drying process. The higher the uneven degree of particle size distribution was, the slower the grain materials were dried and the more unbalanced the moisture distribution appeared.