Abstract: The paper first presents an introduction to China's raw coal washability evaluation criteria and then points out the problems concerning the underutilization at the present stage of the extremely difficultto-wash coal especially the scare coal resources. Then,an in-depth analysis is made of the key points in control of the process parameters involved in heavy-medium separation of the above-cited coal. The research-derived achievements provide a certain technical support for the design of the parameters involved in separation of difficult-to-wash coal with H. M. cyclone in the future.