Abstract: Through the analysis of the causes and hazards of slime water, we analyzed slime water properties and reasons of difficult treatment by the experiment. We studied the coagulation treatment of slime water by precipitation method to determine process conditions. Experimental results show that the tiny particles in water with negative charges are difficult to be naturally sedimentation because of slime water. Treatment effect is good by using carbide slag and PAM slurry, the treated water discharge standard and reuse of coal washing can reach to standard.