Abstract: In order to overcome the difficulty encountered in the treatment of coal slurry at Halagou Coal Preparation Plant,on the basis of the analysis of the feed,underflow and overflow of the thickening pond,a series of measures has been taken for the improvement of the slurry treatment system. These include addition of flocculant preparation system,detection of thickness of the layer of the classified water in thickening pond and increase of capacity of slime recovery equipment. Through the upgrading of the slurry treatment system,the thickness of the classified water layer can maintain in a range of 0. 80 ~1. 50 cm while the coal slurry treatment capacity and the proportion of the small coal treated are increased by 1 638 m³/ h and 20 percentage points respectively. The optimization work has yielded a remarkable result.