Abstract: Due to the similar density of organic macerals in coal, how to effectively separate vitrinite from inertinite has always been a difficult problem in coal processing. Low density heavy medium cyclone is a feasible method to separate vitrinite from inertinite, but because of low density and small solid volume concentration in the system, the suspension is easy to settle and worsen the separation effect. In this paper, the stability and rheological properties of dense medium suspension mixed with fine magnetite powder, low ash slime and montmorillonite powder are discussed. The results show that under the condition of a certain suspension density, the addition of slime can effectively improve its stability in the gravity field, while nearly adding montmorillonite cannot increase the trend of delaying settlement. Due to the synergistic action of magnetite powder, montmorillonite and low ash slime, the heavy medium suspension could form remarkable structure and obtain the best stability. In addition, the heavy medium suspension shows pseudoplasticity in accordance with the power law. The apparent viscosity of the heavy medium suspension mixed with magnetite powder, montmorillonite and low ash coal slime could be as low as about 70 mPa·s at shearing rate of 70.22s-1, and even could theoretically reach as low as 35 mPa·s at shearing rate of 200 s-1, which is more in line with the requirements of low viscosity and good stability of suspension during heavy medium cyclone separation. It means that moderately increasing the ash content of coal slime in heavy medium suspension will be beneficial to the stability of separation.