IsaMill is a high-speed stirred mill that has been newly developed in the mineral industry for fine and ultrafine grinding. In this paper, a numerical model that is based on the discrete element method (DEM) was developed to study particle flow in a simplified IsaMill. The DEM model was validated by comparing the simulated results of the flow pattern, mixing pattern, and power draw with those measured from a same-scale laboratory mill. Spatial distributions of microdynamic variables related to flow structure such as local porosity and force structure such as particle interaction forces, collision velocity, and collision frequency in different regions of the mill were analyzed. The results showed that particles near disks move more vigorously than those close to side walls. Large velocities were observed in the vicinity of the disks, with the tangential component being dominant, followed by the radial velocity. While high collision frequency occurred in the region between disks, high collision energy occurred near disks. Among the three contact forces analyzed, the maximum contact force was more representative and could be related to the collision energy. An attempt was also made to correlate the collision energy and frequency with the measurable variables such as local velocity and porosity. The findings are useful to understanding the flow of particles and its relation to particle-particle interactions and grinding performance in IsaMill.