Abstract: For enhancing the medium stability of the plant's heavy medium separation system, a new design scheme of the automatic process control system is proposed based on the technical features of the existing washing system. Through this system, the regulation of medium density can be effected through integration of process control system and existing centralized control system, and the use of expert experience and traditional PID combined control method while the medium viscosity can be automatically regulated using closed-loop PID control method. As evidenced by qualitative analysis of the performance of the designed control system in practical operation at the plant, the medium density of the heavy medium washing system can be regulated in a timely and effective manner.