The distinct element method (DEM) is a very effective analytical tool for ascertaining the complicated behavior of granular materials. Previous papers indicated that the complex behavior of the granular materials during discharge in silos could be properly simulated using DEM. In an effort to shed greater light on this issue, to explain the dynamic variation in the pressure acting on the side walls during discharge, a model composed of 4000 particles is analyzed, and their behavior and the variation they create in the pressure are examined in detail. The results of this study demonstrated a pulsation phenomenon of the particles in the upper area in the silo, as in the experimental or practical silo, with its period being identical to that of the variation in pressure. Since it is important to explain the time period of this phenomenon, to facilitate the designing of silos, the approximate velocity of the P-wave and the variation in the void ratio were also examined. However, no definite relationship between these parameters and the period of the variation could be found.