Abstract: The slime water prepared with a mixture of high-purity kaolinite and low-ash clean coal is taken as the object of study. The effect of kaolinite on property of the slime water is investigated by measuring the variation of the pH value and electrical conductivity of the water with the content of kaolinite in water, and the single-factor method is used in slime sedimentation experiment. Study result shows that: the pH value and electrical conductivity of the water vary in negative correlation with the content of kaolinite, and when the content of kaolinite remains constant, the electrical conductivity tends to increase with the increase of concentration of the water; the content of kaolinnite, slime water density and amount of calcium chloride used all exert a noticeable effect on sedimentation of the slime water; and a much better sedimentation result can be expected at a room temperature of 25℃, a content of kaolinite of around 10%, a slime water density of no higher than 60 g/L and a dosage of calcium chloride of 0.5~0.7 g/L.