Abstract: According to a narrow effective separation particle size of a coarse slime separator in the industrial liquid-solid fluidized bed and a low separation efficie ncy to difficulty washed coal, a theoretical study on the medium density affected to the separation effect of liquid-solid fluidized bed was conducted and upflow clean wa ter flow in the liquid-solid fluidized bed was replaced with heavy medium flow.Under the two upflow conditions individually, the coarse slime separation experiments of t he liquid-solid fluidized bed with different flow rate were conducted on the coarse slime with particle size of 3 ~ 0.25 mm.The results showed when heavy medium flow was applied to the separation, the separator would effectively have an effective separated particle size scope of the coarse slime expand to 3 ~ 0.25 mm and a deviatio n value possibly would be 0.05 ~ 0.10 g/cm3.Under a high flow rate, the ash content of the clean coal could be reduced to 9.85%. When the ash contents of the clean co al was required not over 11%, the clean coal production rate would be improved by 10.21%.