Abstract: To tackle the problem regarding the unsatisfactory sedimentation effect of coal slurry water at Suncun Coal Preparation Plant, the overflow of the coarse-to-medium-grained slime H.M.cyclone is selected as the object of study.Based on the result of analysis of the slurry water property, the single-factor experiment method is used to explore the effect on slurry water settling rate produced by types, dosage, mixing ratio of agents, and addition of coarse particles.Test result shows that addition of coarse particles has basically no influence on settling rate of slime, and a best slime settling effect can be expected in the case of using coagulant magnesium chloride in combination with flocculant polyacrylamide with a ratio of 4∶9 and a dosing time interval of 3 minutes.