Abstract: It is first demonstrated through analysis of the test data obtained at Datun Coal Preparation Plant that there exists a positive correlation between the ash and density of gangue contained in raw coal,and based on the finding,a regression equation is,hence,derived.This makes it possible to make a quantitative description of variation of ash in relation to density of gangue.As evidenced by result of analysis of test data,coal and gangue in raw coal feed are two kinds of minerals with different properties,and their attributive regression equations differ with each other in interception and slope.And it is found that the regression equation for derivation of density of gangue has a larger slope and a much larger ampritude of variation of ash with density.Therefore,the two equations are not to be used as a substitute for each other.