Abstract: Because of the rise of proportion of finer coal in raw coal, the heavy medium separation system of the Liyang Coal Preparation Plant is facing a series of problems in operation such as instability of separation density, high medium consumption, high concentration of circulating water, low flotation efficiency and low yield of clean coal. To address the issue, test on sedimentation of the slurry of the plant is conducted with the methods of natural sedimentation, and promotion of sedimentation with the use of flocculant, coagulant and combined use of flocculant and coagulant, with an aim to determine the optimal slurry water treatment scheme. Test result shows that when calcium chloride is first added at a dosage of 400g/m³ (agitation time: 30s) followed by the addition of anionic polyacrylamide (PAM), a best sedimentation result can be expected, and the settling rate in this case is up to 72.48cm/min.