The utility model discloses a medium density automatic control system of dense medium separa tion factory, including medium density master control system and monitoring host, a serial communication port, density sensor, magnetism thing sensor, level sensor, add the water regulating valve, pump control module and reposition of redundant personnel control mechanism, add the water regulating valve, density sensor and magnetism thing sensor are all installed on the medium pipeline that is situated between the bucket and closes jie's pump is closed in the connection, level sensor installs in closing the bucket that is situated between, reposition of redundant personnel control mechanism sets up in the current divider box below, density sensor, magnetism thing sensor and level sensor all meet with PLC control substation, PLC control substation and monitoring host meet, PLC control substation still with add the water regulating valve, the pump control module is met with reposition of redundant personnel control mechanism. The utility model discloses overcome artificial regulation density and the unable defect that realizes accuracy, rapidity of control coal slime content, alleviateed intensity of labour, improved raw coal wash -out rate.