Abstract: According to the high ash fusibility coal from Huainan and Huaibei Minng Areas was hard directly to apply to the available liquefaction technique with th e liquid fly ash discharging, under the weak reduction air, the 5E-AF I intelligent ash fusion detector and X-ray diffrarctometer were applied to study the ash fusion char acteristics temperature and the high temperature fly ash fusion crystal mineral composition of LH1, LH2 and LH3 typical coal samples with calcium base flux.The study「 esults showed that after the calcium base flux added, with the steadily added quantity of the flux, the ash fusion temperatures of the three coals would be in three differ ent variation tendency as a first increasing and then reducing, a first reducing and then increasing and a first reducing, then increasing and late then reducing.As for the coal LH2 with the calcium base flux added, the fly ash would form the anorthite and low ash fusion temperature mineral when the temperature reached at 1 200。C whic h could restrain the formation of the mullite and could reduce the ash fusion temperature.Due to the X-ray diffractometer could be not well applied to explain the differen t variation tendency of the ash fusion temperature after the calcium base flux added, thus the combination of the basic chemical composition and the ternary phase diag ram of the fly ash were applied to further discuss the fly ash fusion mechanism after the calcium base flux added.