Abstract: The security of grain storage is a worldwide issue, which is related to the economic development of the country and social stability. Porosity is an important factor affecting the migration of moisture and heat in grain piles. In order to obtain the distribution of porosity and density of stored grain piles under different vertical pressures, a self-made grain porosity measuring instrument was used to study the porosity of indica rice, japonica rice, wheat and corn under the pressures of 0, 52, 104, 146 and 208 kPa. A grain pile pressure-porosity relationship model was established. FLAC^3D is used to model the test chamber with full scale. Based on FLAC^3D numerical simulation pressure field data and experimental results, the spatial porosity and density distribution of grain pile in grain warehouse were studied, which provided a reference for the analysis of grain pile coupling theory in grain warehouse. The test results showed that with the increase of vertical pressure, the porosity of the four grain piles decreased in a power function, the R² value of the fitting curve of pressure and porosity of each grain was greater than 0.95, indicating that the model can accurately describe the porosity and density distribution of grain pile under different pressures. While, with the increase of vertical pressure, the density of grain pile increased. In detail, when the vertical pressure of grain pile was in the range of 0-208 kPa, the porosity of four grain was in the range of 49.80%-35.62%, and the density was 524-886 kg/m³. For different crops, when the vertical pressure of grain pile was 0-208 kPa, the porosities of indica rice, japonica rice, wheat, and corn were 49.80%-42.28% 47.90% to 40.72%, 40.63%-35.90%, and 40.00%-35.62%, respectively. Rates of change in porosity of indica rice, japonica rice, wheat and maize were 17.79%, 17.63%, 13.18%, and 12.24%, respectively. Therefore, with the increase of vertical pressure, the porosity of grain pile of japonica rice and indica rice changed rapidly, followed by wheat and corn. And the grain piles densities of wheat and corn were higher than those of japonica and indica. Moreover, the porosity of horizontal and vertical grain pile in grain warehouse were symmetrically distributed and both the porosity and density of grain pile were stratified in the vertical direction of grain warehouse. In the horizontal and vertical center vertical plane of grain warehouse, the average porosity of the top and bottom grain pile was 40.63% and 38.84%, and the density was 822 kg/m³ and 846 kg/m³. When the depth of the grain pile was less than 1 m, the average rates of change in porosity and density of grain pile were 1.1% and 0.74%, respectively, and when the depth of grain pile was 7-8 m, the average rates of change in porosity and density of grain pile were 0.32% and 0.21%, respectively. In the horizontal direction of grain warehouse, due to the influence of the wall friction, the porosity distribution of grain pile showed "mall center, large surrounding", the density distribution of grain pile is "large center, small surrounding". The research results can provide theoretical support for the optimization design of the granary ventilation system, and provide a reference for the grain clearance and inspection.