Abstract: Grain pile is a kind of non-consolidated hygroscopic porous medium and its internal pore structure is complex and diverse. During the drying and storage of grain pile, the heat and mass transfer inside the grain pile mainly occurs in the pore space surrounding grain particles and the interface between pores and particles. The simulation results of traditional model based on the "continuous medium hypothesis" can reflect a general trend of heat and mass transfer rather than the transfer phenomenon between particles and pores. In fact, the simulation results of heat and mass transfer between particles is far from the actual drying conditions. In detail, no difference is found between the state parameters of pores and particles, which is inconsistent with the actual situation during the drying process of grain pile. In order to determine the positional relationship of skeletons and pores in the unconsolidated porous medium more accurately, and describe the heat and mass transfer of unconsolidated porous medium during the ventilation process more reasonably, an irregular pore network model was constructed to describe the internal structure of grain pile. First of all, 3D CT scanning equipment and Avizo software was used to extract the pore throat of the particle accumulation sample. It was found that the length of the throat is mainly distributed between 6.0 and 14.0 mm, accounting for about 96% of the total throats, and the distribution of throat length roughly fits Poisson distribution; the pore radius is mostly between 2.0 and 10.0 mm. Secondly, according to the principle of Tyson polygonal structure, the natural accumulation process of grain particles was simulated by EDEM software. The particle information was processed by voro++ software. Combined with the pore division rules, some obtained pores were merged to optimize the pore network. The three-dimensional irregular pore network physical model was built to describe the pore structure of grain pile. The pore coordination number is mainly concentrated in 3, 4, 5 and 6, the throat length is mainly between 3.0 mm and 13.0 mm, the pore radius is roughly between 2.0 mm and 10.0 mm, and the three parameters roughly fit Poisson distribution. The results also showed that the obtained structural parameters are more exhaustive than that of Avizo software. The three-dimensional irregular pore network physical model is able to describe the relationship between particles, pores and throats in the storage grain pile more precisely.