Abstract: To tackle the problem regarding the high content of dirts in raw coal, Xiaohezui Plant opts for the use of the air separator for preremoval of gangue from raw coal, based on result of analysis of property and both size and density composition of raw coal. It it indicated that through analysis of both technical and economic performances of the process, at a separation density of 1.77 g/cm³, the E_pm is 0.165 g/cm³, with the yield and ash of clean coal being 40.75% and 47.23%, respectively; the loss of coal in discards is 8.99% with the <1.4 g/cm³ density fraction in a proportion as low as 1.36%; and the separator can work with a gangue removal rate reaching 77.87%, saving 4.175 million yuan for the plant per year. The use of the separator proves to be effective for reducing content of dirt in saleable coal and can yield significantly favorable economic result.