Dense Medium Drum (DMD) separation is applied particularly in the coal and recycling industries. Characteristic of the process is a separation based on density, driven by the buoyancy and gravitational forces acting on an object moving in a free surface flow. The fundamental phenomena occurring in a DMD have been widely investigated by (Napier-Munn, 1991). However, in contrary to other separation methods, such as the Dense Medium Cyclone which was investigated extensively by (Kuang et al., 2014) and others, no Computational Fluid Dynamics (CFD) studies have been conducted for the DMD separation. Even recent studies, like (Meyer and Craig, 2015), use first order models which need to be calibrated with performance data of the investigated drum. Hence, important parameters like the flow-velocity and the detailed design of the drum are only taken into account indirectly. This paper reports a detailed CFD analysis of the flow in a generic DMD separation process. The study comprises, a general understanding of the flow field and an analysis of the impact of different process parameters. Furthermore, the model predicts the actual separation performance of the DMD at different working points. To the authors’ knowledge, this is the first study which conducts a CFD analysis of a DMD separation process. Therefore, findings concerning the flow field and its influence on the separation efficiency will be reported on. Moreover, the separation model can be used to derive the coefficients for highly used first order models without the need of experimental data. Like this, the early design phase of DMD separation processes can improve immensely.