Abstract: In order to improve the medium density control precision of the existing heavy medium separation system, work is made on the technical transformation of the medium suspension density control system based on PLC centralized control technology for effecting automatic regulation of suspension density, control of content of coal fines in suspension and control of liquid level of qualified medium tank. Practice shows that the technical transformation has led to noticeable improvement of medium suspension density control precision, and reduction of medium loss and consumption in coal separation.