Abstract: The effect of kaolin on the ash fusion characteristics of high alkali Xinjiang Zhundong coal was investigated by quantum chemistry calculation and experimental measurement methods. The results show that the ash fusion temperature is increased significantly by adding kaolinite; the ash fusion temperature increases rapidly at first with the increase of kaolinite content added in the Zhundong coal and then levels off when the fraction of kaolinite exceeds 10%. By adding kaolin in the Zhundong coal, the content of minerals with a low melting point (1 100-1 200 ℃), such as anorthite and anhydrite, is reduced, whereas mullite is found at 1 200-1 300 ℃. O (26), Si (6), O (22) and Si (8) atoms in the kaolinite molecular structure exhibit relatively high reactivity; Al-O bond, which is connected with O (26) and O (22), can be ruptured by reacting with Fe²⁺ or other metal ions in ash as an electrophilic reagent. The O^2- of alkali oxides in ash, such as Na₂O and CaO, can react as a nucleophilic reagent with Si (6) and Si (8) in kaolinite, breaking the oxygen bridge bond of Si-O-Si in kaolinite.