Mechanical ventilation is the main measure of ensuring the grain’s safety and quality.The mechanical ventilation of the grain storage in warehouse can be divided into the horizontal ventilation and the vertical ventilation.The ventilation resistance varies with different grain variety and grain bulk.According to Computational Fluid Dynamics（CFD）method，numerical simulation analysis of horizontal ventilation and vertical ventilation resistance of three kinds of grains（wheat，paddy and corn）in grain bulk is conducted.The foundation for the fan selection of the mechanical ventilation system and the optimization of ventilation system was laid through the comparison between the ventilation resistance under different grains’ ventilation pattern and the experimental data，with the analysis of its grains’ layer resistance variation.