Abstract: To improve the separation accuracy of coal preparation plants, this paper proposes an automatic control scheme for ash content of clean coal in dense medium separation. Firstly, the overall framework of the system is introduced, and then the design of core modules including online ash content detection, ash content prediction, SPC analysis and closed-loop control algorithm are elaborated. Finally, the field application is carried out to verify the system performance. The application results show that after adopting the automatic control system, the ash content of clean coal is steadily maintained between 10.6%～11.2%, which meets the technical requirement of 10.5%～11.5%. The system has large-scale promotion value and can provide technical reference for quality improvement and separation optimization in coal preparation plants.