Abstract: In order to reduce ash of flotation concentrate of hard-to-separate and high-ash coal in Wuhai mining area of Inner Mongolia,effect of slurry mixing time and froth layer thickness on ash of concentrate is analyzed by timed-release analysis of coal slime flotation,at the same time,studied ash reduction result of grinding and flotation technology. The test result shows: high ash of flotation concentrate is mainly caused by non-selective floating upwards of high-ash fine slime and medium-density intergrowth,while flotation selectivity isn’t improved by scrubbing of high turbulent flow on mineral particles,but thick froth layer can prevent high-ash fines mixing in concentrate. The better flotation concentrate with 14. 98% ash and 61. 02% yield is obtained under the condition of grinding in 0. 5 min,slurry concentration of 80 g/L,mixing intensity of 1 800 r/min,aeration volume of 0. 25 m³/（m²·min）,dosage of 600 g/L diesel and 100 g/t octanol 2.