According to the heat balance principle, the boiler thermal calculation model based on the on-line operating data is presented. The on-line data filtering pretreatyment are built into the system. Effect of coal and boiler load variation are also taken into account. From the point of ecoomic operation of the unit, adequate detenmination of the desired cleaning factors are discussed in detail. This paper presents the design and implementation of an ash monitoring and sootblowing advisosry system for the 300 MW coal-fired boiler in Hengshui Power Station