Ventilation resistance characteristic of grain layer is the key influence factor to the drying uniformity and energy consumption, is also the theoretical foundation parameter for layer design and fan selection. The traditional empirical formulas of ventilation resistance of grain layer are low precision and ignore the complicated changes and nonlinear uncertainty problems of grain layer porous media. The pressure loss factors were discussed based on the traditional Ergun model. By testing the airflow resistance on test platform, dividing the air velocity into subsections by the exploratory analysis method, and introducing an error influence factor λ, a new pressure field model of variable layer was derived based on the Ergun model. The optimal resistance characteristic curve was given, and the relationship between the ventilation resistance and layer thickness was built. The results show that when the air velocity is less than 0.2m/s, the λ is 1; when the velocity is between 0.2m/s and 0.4m/s, the λ is 0.89; and when the velocity is between 0.4m/s and 0.6m/s, the λ is 0.79.