Abstract: In view of the drawbacks of artificial sampling and preparation process and the online coal ash determination devices currently available on the market, the DF-5756A passive ash monitor is introduced. A description is made in the paper of the make-up, working principle and the technical and display features of the monitor, as well as the points requiring attention in its use. Experimental study shows that the monitor works remarkably well at Zhenchengdi Mine Coal Preparation Plant with its accuracy and performance well up to the specified standard and requirement.