Abstract: The raw coal with extremely difficult washability is separated by 3GHMC1500/1100 gravity-fed three-product heavy medium cyclone in panyi coal preparation plant and particle size and density distribution of products is analyzed. By evaluating its process,it is concluded about technology index of cyclone that imperfection of first stage of cyclone is 0. 020 kg/L and total misplaced material is 5. 15%,as for second stage,imperfection is 0. 029 kg/L and total misplaced material is 1. 27%; ash error and organic efficiency is 0. 42% and 93. 20% respectively.