Abstract: Based on the application of flip- flow screen in deep classification of steam coal,the optimization of process was introduced. For the coal preparation plants which prepared the whole grade steam coal,the application decreased the slime production,made the fine coal separate in lump coal separation system or fine coal separation system flexibly,let the pulverized coal go into water wash system or be sold as fine coal. For the coal preparation plants which only prepared lump coal,the application reduced the lower limit of separation,increased the separation amount of the lump coal,realized- 25 mm steam coal could be separated by dense medium shallow slot cyclone.