The element and mineral composition and the physical characteristics of fly ash from circulating fluidized bed boiler, are different to the other kinds of boilers. The aim of the study was to discuss the distinctive feature between the fly ash from CFB and the fly ash from pulverized coal fire boiler. The experiments show that the change of element composition from CFB and PC boiler has the some rule with the change of granularity. The carbon content of residua from CFB is higher than the content from PC boiler obviously. The SiO 2 dioxide content decreases with the granularity of residua fining, while the content of Al 2 O 3 , CaO, MgO has the reverse rule in despite of CFB or PC boiler. The content of TFeO of residua increases in CFB while the content decreases in PC boiler with the granularity of residua fining. And the component form of TFeO in CFB is mainly Fe 2 O 3 while the component in PC boiler is mainly Fe 3 O 4 . The higher the content of carbon was, the lower the special resistance was.