Abstract: Based on the original data of the raw coal feed and products obtained through washing with a stand-alone H.M. cyclone, 48 regression equations expressing the positive density-ash correlations of different coal size fractions with a nearly the same intercept a and slope b are derived through regression analysis, and the results obtained are checked through t-test with the method of mathematical statistics. Result of analysis shows that the density-ash regression equation of the 50-0.5 mm composite size raw coal feed with a density ranging from 1.60-2.10 kg/L can be used to predict the density of various size factions of coal.