Aiming at the short drum system in which only one end face can rotate with the side wall in the slag crushing process, the discrete element method (DEM) is used to simulate and study the influence of the drum length-diameter ratio and rotation speed on the axial flow characteristics of granular materials. Simulation results indicate that distinct axial convention occurs inside the system: particles in the upstream zone tend to move towards the fixed end-wall side, whereas those in the downstream zone are apt to shift towards the rotating end-wall side. At low rotating speed condition, along the transverse direction the axial velocity profile of particles at the free surface presents an asymmetric characteristic. The axial velocity magnitude of particles in the upstream zone is clearly smaller than that of particles in the downstream zone. The axial velocity magnitude of particles in the two zones reaches the maximum value at y/R=±0.725, and the position where the axial velocity is 0 does not appear in the tangential middle position. Such asymmetric characteristic is nearly independent on the axial length of the drum, whereas increasing the rotational speed of the drum will increase the axial velocity of the particles and gradually reduce this asymmetry. Changing the rotating speed of the drum has a greater effect on the axial flow of particles in the upstream zone of the material than on the axial flow of particles in the downstream zone. When the length-diameter ratio of the drum reaches 1.2, the influence area of the rotating end-wall on the axial flow of the material will not change significantly with the increase of the rotating speed of the drum. The simulation results thus provide helpful guidelines for the future optimization of the real drum system used for particle milling.