Abstract: The problem faced by Sanhekou Coal Preparation Plant is that the PID-controlled system for control and adjustment of the correct medium density in the process of coal cleaning using heavy medium cyclone is limited in capacity. To tackle this problem, a system identification-based mathematical model is developed based on historical correct medium density and clean coal ash data.The density of correct medium can be dynamically adjusted using the sophisticated model predictive control algorithm for improving density control accuracy and hence the efficiency of H. M. cyclone. Practice shows that the use of the method can yield a remarkable density control result and lead to effective restraining of random interference in heavy medium separation process, and stability of density of correct medium. Moreover, the ability of making dynamic density adjustment makes it possible to make noticeable upgrading of clean coal, drastically reduce fluctuation of clean coal ash and improve economic performance.