Abstract: In this paper a novel digital low"-energy γ--ray ash monitor is described indetail. It is a by--line industrial ash monitoring instrumentation capable ofeffecting continuous, automatic, rapid, and accurate measurement of the ashcontent of the jig clean coal in less than one minute. The measured value corres-ponds well with the analytical value with the MSR error better than 0.5%(absolute value). In industrial application, it can basically meet the requirementof monitoring the quality of the jig clean coal and timely guiding the washingprocess.