Silo, a very popular structure in powder and mining industry, is a vertical container with an open outlet at the bottom and an optional inlet at the top. The design of silo requires a deep understanding of stress distribution at boundaries in both static and dynamic condition. Prior numerical studies use Finite Element Method or Finite Difference Method which shows an increase of vertical stress before it is leveled out by friction at a shallow depth. This is understandable for continuous media because the settlement caused by vertical stress must stop at some level. Nevertheless, experimental studies show that the vertical stress of the granular and porous media still increases with a constant rate even at a much greater depth. Although the Discrete Element Method (DEM) can simulate granular materials, it has some difficulties in determination of stress distribution because it is based on contact force, not the stress. This paper employs DEM with sphero-polyhedra shapes to simulate the behaviour of granular materials in silos. The stress distribution is calculated as average values. This requires a significant number of particles. Therefore, the paper focuses on narrowly graded materials. Some correlation with experimental data has been found.