Abstract: Adjustment of coal ash fusibility of high fusion point coal has been attracted by attention of many researchers in coal gasification and combustion. The effect of Mg²⁺ and Na⁺ on the fusibility behavior of the high fusion temperature coal ash from Yangquan Guzhuang was studied in this paper, using the method of adding different amount of MgO and Na₂CO₃ (5%~25%) to the coal ash. The result shown that the ash fusion temperature monotonically decreases with increasing addition amount of MgO, while the ash fusion temperatures exhibit low valley and reach the minimum when the addition amount of Na₂CO₃ is 15%. Investigated by XRD, mullite and cristobalite are detected in the Yangquan Guzhuang coal ash, which results in the ash fusion temperature of the coal ash higher than 1 750℃. Additions reacting with silicate minerals can form more low-melting eutectic minerals, such as cordierite and nepheline, etc. Meanwhile, the additions of Mg²⁺ and Na⁺ cause non-bridged oxygen and oligomers increasing, then the ash fusion temperature reduce. Ternary phase diagram and SEM micrograph confirm that the local clustering of partial elements and reunited phenomenon of coal ash under high temperature condition result in the different effect of Mg²⁺ and Na⁺ on the coal ash fusibility behavior.