Abstract: In order to solve the problems arising from rapid determination of ash content of coal by artificial means, the passive online ash monitor is used by Zhaiyadi Plant to measure the ash contents of both raw and clean coal, and an online measured ash data-based intelligent medium density control system is developed. Field application of the system has yielded a favorable economic result as evidenced by the facts that the ash content of the clean coal product of the plant's heavy medium separation system has seen a little rise from 9.5% to 10.0% yet its yield is increased noticeably by 0.5 percentage points.