Abstract: The ash fusion characteristics of Shenfu coal (A), sewage sludge (W1), modified sewage sludge (W2) and the mixture of coal and sewage sludge (AW1, AW2) were studied. The Shenfu coal with the addition of W1and W2 has lower fusibility temperature than coal and sludge. When 30.74g W1 ash is added to A ash, the ash fusion temperature reduces by 63℃ and reaches the lowest point, and when  51.23g W2 ash is added to A ash, the ash fusion temperature decreases by 82℃ and reaches the minimum. The analysis of the mineral matter of coal, sewage sludge and mixture was conducted by XRD diffractograms and the transformation of mineral matter in the mixture of AW1, AW2 at different temperatures was compared. The result shows that chloroapatite is formed and the transformation temperature of quartz, anhydrite, and hematite decreases when W1 is added to coal; while plenty of sodium in W2 and the transformation of sodiummineral matters in WA2 coalsewage sludge mixture at different temperatures are the main reasons for the lowering of ash fusion temperature.