Abstract: in order to improve coal separation acuracy of heay mediumn cyclone the paper analyzed raw coal density composition,paricle size compositlon.coal feeding size and sta lityraw cal mudding property and others affced to cal separation ef ct of heary mediun cyclone. The analysisresults showed that density compostion varato of rav cal fed and unstable coalfeeding value would cause separaion density fucuation of heavy mediun cyclone and would reduce separation efficiency. The finer paricle size,the worst separation eff ct of raw coal would be.The actual separation densty of fine parices generall woula be igherthan the actualseparation density of the coarse paricles. When feeding value was over raed feeding value the separaton eficency of cy.lone would be reduced and the clean coal production would be reduced.When raw coal was mudding,the separation effect of heavy medium cyclone would be worst obviously