Abstract: In order to solve the high ash content which will influence the final cleans ash index, we carry on experimental study on flotation column of coal slime in Zhaozhuang coal preparation plant. The influence of three variables such as inflating volume, pulp density and frother dosage on the test indexes of flotation column was also studied by Gauss-Midgley method. The results showed that the optimized value of three variables was 1.8 m³/h of inflating volume, 60 g/L of pulp density, 200 g/t of the frother dosage in the separation process of Zhaozhuang coal preparation plant, the yield and ash content in the best separation conditions was 75.11% and 10.89% respectively.