Abstract: Owing to the nature of raw coal in Zijin coal preparation plant is high ash content,high fine particle and refuse easy to sliming,as well as flocculent adding of tailings thickener by artificial adjusting,the turbidity of overflow is instable and often over criterion,even out of control.For this reason,the automatization reformation for flocculent adding system was implemented.A 3-point turbidity detecting method in thickener defecated water was put forward,and a fuzzy controller was designed with an input of turbidity change rate along the deepness of thickener defecated water,and a flocculent automatic adding fuzzy control system was developed.Industrial test results turn out that after reformation the turbidity of overflow water meets its basic requirements,as well as its stability and the quality of cycle water were improved evidently.Moreover,the flocculent consumption was reduced.