Abstract: A study is carried out in the slurry recovery system of Majialiang preparation plant of Datong Coal Mine Group. The particle sizes of the overflow of classifying cyclone, the underflow of waste coal high-frequency vibrating screen and the coal slime to be filtered by pressure filters are analyzed and the reasons to the problem that the coal slime contents high ash are discussed. As for the slurry to be filtered, the hydrocyclone is used in the study of reducing its ash by gravity separation. And as to primary slime, flotation effects of many agents on it are compared and studied. Finally, three methods to reduce the ash of coal slime in the steam coal total preparation plant are found, which are pressure filtration of coal slime with high ash separately, gravity separation of coal slime and flotation of coal slime with good quality flotation agents.