Abstract: Aiming at the limitation of coarse slime separation in traditional liquid solid fluidized bed, the authors proposed that improving density of separation medium by adding in heavy-medium, which can make the wide size materials based on density separation. Experimental study on coarse slime separation effect were carried out under different bed pressure and water velocity conditions in heavy medium liquid solid fluidized bed and the conventional liquid solid fluidized bed. The results showed that in the same rising water velocities and different bed pressure ,after adding the medium, the E value of the possible deviation can be decreased by 0.070 when the medium is not added, the quantity efficiency is increased by at least 4.43%, when the ash contents of the clean coal was required not over 10%, the clean coal production rate would be improved by 5.2%. Under the same bed layer pressure and different water velocity conditions, the E value of the possible deviation can be decreased by at least 0.030 after adding the medium, the quantity efficiency is increased by at least by 1.87%, when the ash contents of the clean coal was required not over 10%, the clean coal production rate would be improved by 1.79%. The sorting accuracy and the separation effect were significantly improved.