Abstract: This paper mainly analyzed the reason why high ash fine coals are difficult to be floated and discussed the current separation techniques. The main conclusions are as follows: the entrainments of high ash fine slimes is the main cause for contamination of concentrates, especially the clay minerals. Furthermore, slimes coating cause a deterioration in coal floatability and making a portion of low ash coals sink into tailings which may cause a loss to the combustible recovery. Moreover, high ash fine slimes has a damaging effect on floatation process because of the increasing reagent consumption. The current separation technologies consist of rougher-cleaner system, desliming floatation, classified flotation, branch flotation, high shear conditioning and depressants etc, the desliming floatation and classified flotation has a distinct advantage. The above technologies obtained a certain effect, but a further research is needed.