Abstract: Mineral matter transformation is an inevitable process in coal ash combustion or gasification. The rule of thermal conversion directly affects the melting and deposition behavior change of coal ash in the furnace, which also determines the applicability of coal. To reduce the loss of minerals in coal ash and the volatilization of alkali metals, four kinds of Xinjiang coal ash were prepared by low temperature ashing method, and cold water quenching method was used to avoid the change of coal ash crystal phase during the cooling process. Then X-ray diffraction (XRD) and X-ray fluorescence (XRF) spectrometer were applied to analyze the heat transformation of coal ash in heating and cooling process. The results show that thermal decomposition of calcite and anhydrite is an important transformation process of the four coal ash, and quartz reacts with other minerals as the temperature increases, and the content of quartz decreases greatly and new crystalline phases are formed. The chemical composition has a great influence on the mineral types of coal ash. The Qiketai and Heishan coal ash with higher Ca content is easy to generate anorthite and gehlenite, and the anorthite content reaches the maximum at about 1200 ℃. The coal ash with high Fe content in the eastern and western Beitashan regions mainly underwent the transformation process of Fe₂(SO₄)_, hematite, hedenbergite and magnesioferrite during the heating process. At 1400 ℃, most of the crystalline phases were almost disappeared, and only the high-melting point magnesioferrite crystal phase existed. The volatilization rate of alkali metal Na reached the maximum at 800–1000 ℃, and the overall rate was increased first and then decreased. Compared with the heating process, the crystalline phase in the cooling process remains basically unchanged, but the crystalline phase strength increases.