Abstract: Aiming at the coal slime that is characterized by high content of kaolin,large amount of micro- fines,difficult settling in kaida coal preparation plant of Inner Mongolia,settling effect of coal slurry from this plant was studied by using nine different coagulating agents. The test results show that coagulating agent Al Cl₃ is the most appropriate for this coal slurry; the best settling effect is obtained by orthogonal experiment when the dosage of Al Cl₃ is 6 g / L,stirring 30 s at a speed of 80 r / min.