Abstract: The on-line monitoring of ash and moisture of coal is affected using natural ray and microwave methods respectively.The paper presents an introduction to the working principle,structure and functional features of the passive monitor,as well as an evaluation of the results obtained through the use of the monitor for on-line detection of quality of both cleaned and raw coal.Practice shows the monitor works in an environmentally-friendly manner without the use of radiation source,and is high in accuracy and automation level,and the ash and moisture values detected can serve as a basis for guiding the production of clean coal products and making internal economic accounting.Therefore,a favorable socio-economic result is yielded thanks to the upgrading of coal products,curtail of management cost,increase of efficiency and reduction of number of personnel.