Abstract: According to the problem of high ash content and low yield of clean coal floated from difficult to wash slime in Kailuan mining area,analyzed its native and actual floatability and conducted the flotation speed test,also analyzed size distribution of flotation products.The test results showed that the best native floatability is the 0.25-0.125 mm middle particle size,the 0.5-0.25 mm and 0.125-0.074 mm size fraction in the second place,and the ＜ 0.074 mm size faction is poorest,but due to the large specific surface area,this size fraction priority absorb the agent in flotation process,,then lead to actual floatability stronger and speed the velocity of flotation,caused high-ash slime entrained in flotation concentrate.