Abstract: The understanding of sintering temperature of coal ash is of significance for the design and operation of fluidized bed combustion and gasification systems. So the ash sintering for different coal ash samples under different reaction atmospheres was studied by means of a coal ash sintering temperature measuring system based on the variation of the pressure-drop, and the effects of reaction atmosphere and ash composition on coal ash sintering behavior were discussed. The results show that the sintering temperature increases with the ratio of the acidic oxide to the basic oxide in coal ash, and an increment of iron in coal ash will decrease the sintering temperature obviously. The sintering temperature of coal ash under reducing reaction atmosphere is lower than that under oxidizing reaction atmosphere, and the sintering temperature under CO atmosphere is higher than that under H₂ atmosphere because an eutectic substance of Na₂S-FeS can be formed easily under H₂ atmosphere for the coal ash including Fe₂O₃、Na₂O and SO₃. The coal ash sintering temperature under typical fluidized bed gasification atmosphere is between that under CO atmosphere and H₂ atmosphere, which is closer to the sintering temperature under CO atmosphere.