Abstract: A homemade pressurized pressure-drop measuring device and X-ray diffractometer (XRD) analyzer were used to determine the effects of alkali catalyst addition and different chemical compositions of nine kinds of coal ashes on the ash sintering temperature. The results show that the sintering temperature of WJT coal ash containing higher Fe and Ca compositions declines markedly after adding potassium carbonate catalyst. K minerals react easily with Fe and Ca minerals to produce low-melting-point eutectics, which accelerates the sintering and agglomeration. The sintering temperatures of various coal ashes are closely related to the contents of Si, Al, Fe and Ca in coal ashes. The sintering temperatures increase for the coal ash with higher content of silicon and aluminum, but decrease for the coal ash with higher content of calcium and iron in ash. Adding K catalyst can promote the slagging by forming eutectic matters, especially in the presence of calcium and iron. The three-element phase diagrams of CaO-SiO₂-Al₂O₃, FeO-SiO₂-Al₂O₃ could explain the sintering temperatures variance.