Besides the coal properties

the slagging in coal- fired boiler furnace is related to the furnace structures and operating pa- rameters. Considering the slagging influence of aerodynamical field and temperature in furnace

two slagging assessment new indexes are put forward-the highest dimensionless furnace temperatare and the dimensionless actual imagenary circle diameter in furnace. In combination with the four indexes of coal properties

the two new indexes are used to set up a com- prehensive slagging assessment model on basis of fuzzy mathematics

this model has been used for prognosis of several large boilers’ slagging

giving a good results.