The temperature and moisture in grain silo changed along with time was researched by means of numerical simulation. In the process of simulation，the real grain storage silo was simplified, thereby a similar physical model was established and compared with the classic experiment, the reliability of the model was validated. Based on local heat and mass balance principle and volume average method, different initial temperatures in grain stack were analyzed by numerical simulation. The variation of temperature and moisture was obtained. When the temperature difference increased from 20 ℃ to 40 ℃, the moisture and temperature in the grain silos also changed significantly. The results of the study provides scientific basis for preventing mildew and moisture condensation during grain storage.