Abstract: Effects of temperature, atmosphere and residual carbon on melting behavior and mineral transition mechanism of fine ash from Chiping and Suqian circulating fluidized bed gasifier at high temperature was studied using fusion point analyzer, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results show that ash fusion temperature of two fine ash is the lowest under reducing atmosphere. The existence of mullite is the major reason for the higher ash fusion temperature of Suqian fine ash than that of Chiping. The ash fusion temperature increases with increasing mass fraction of residual carbon. When temperature is above 1300℃ and the mass fraction of residual carbon is more than 3%, moissanite is formed in slags of both fine ashes. Moissanite is mainly responsible for the worse fusibility of ash with higher content of residual carbon.