The dense medium cyclone is mainly used for density separation in coal preparation production. The accuracy of separation density adjustment will affect the separation efficiency, product ash content and clean coal yield. In this paper, the flow field characteristics, medium density distribution and particle motion mechanism in the heavy medium cyclone are analyzed by using the theory of fluid mechanics, particle dynamics and medium rheology. On this basis, this paper forms a theoretical model including steady-state separation density calculation model and dynamic density control model. The model couples many factors such as medium concentration, rheological properties, feed pressure, equipment geometric parameters and particle properties to form a prediction expression of separation density, and analyzes the sensitivity of parameters. It is found that the medium density gradient caused by centrifugal concentration effect will affect the actual separation density, and the density adjustment range can be expanded by adjusting the particle size distribution of the weighting material and the structural parameters of the equipment. In this paper, the model is verified in the comparison of laboratory small cyclone test and industrial field data. The predicted value is in good agreement with the measured distribution curve, indicating that the model has reliability and applicability. The theoretical model provides a scientific basis for the precise control of the separation density of the dense medium cyclone, which is beneficial to improve the stability and resource utilization of the coal preparation process, and lays a theoretical foundation for the development of intelligent control system