Abstract: The problem with the heavy medium separation system is that the clean coal is made unable to be recovered to the maximum extent because of the poor liberation effect of the system′s raw coal feed. To tackle this problem, an in-depth study is made of the crushing size of the feed in a way as follows: first crush the raw coal to different sizes and then carry out quality analysis of the product that can be obtained in each case based on screening and float-and-sink analysis data. Result of analysis shows that when the raw coal is crushed down to a size with an upper limit of 25 mm, the yield of low-density material is significantly increased indicating that an effective improvement of clean coal yield can be expected thanks to the thorough liberation of raw coal.