Abstract: The problem faced by Longyu Coal Preparation Plant is that the ash of the clean coal product of the primary washing system has to be reduced more than necessary level because of undercapacity of the flotation system. Through systematic analysis of the situation, the plant opts for the use of the flotation cell + flotation column combined system, and semi-industrial test is conducted with the system in order to find out an appropriate flotation process which is well suitable for the treatment of the coal. Test result shows when the ash of the concentrate product is lower than 14% and that of the tailings is higher than 65%, a middlings product with an ash of around 40% is produced. Use of the flotation system optimized based on test result can lead to a drop of yield rate of tailings by 3.33 percentage points, a rise of the yield of the total clean coal product by 2.15 percentage points, an increase of sales income by 21.75 yuan per ton of raw coal, and an increase of annual economic revenues by 43.50 million yuan.