Based on the theory ofheat and mass transfer in porous medium the mathematical model of natural convection and coupledheat moisture transfer ingrain bulk was established. Theheat transfer and natural convection processes and their influence factors were studied by the method of approximate analysis and numerical simulation. The results showed that the temperature was mainly affected by theheat transfer in cereals of small kernel, such as wheat, while for cereals of larger kernel, such as corn, natural convection was the main effect. The theoretical analysis and numerical simulation proved that the effect of low moisture migration ingrain bin on the temperature change ofgrain was very small, which could be neglected. In silos, the effect of natural convection was significant, which enabled the temperature in silo more uniformity.