Abstract: The Baodian and Nantun coals are of high ash fusion temperature. The ash fusion characteristics of the two coal samples were studied by adding fluxes calcium oxide and ferric oxide. By using Xray diffraction(XRD),scanning electron microscope(SEM) and thermodynamic softwares FactSage, the mineral composition and mineral transformation of two ashes by adding different species and mass of fluxes at high temperature were discussed. The results indicated that under the weak reduction atmosphere，the two fluxes can remarkably decrease the ash fusion temperature. Ash fusion temperature showed different change tendency by adding different species and mass of fluxes.