Abstract: in order to study the sedimentation characteristics of kaolinite,which is the hardest handling clay minerals in coal slime water,and the effects of instability of suspension,the Zeta Potential Meter and Turbiscan Stability Analyzer were used to investigate the effects of the concentration of coal serieskaolinite,the concentration of cations and the kinds of cations on stability of kaolinite suspension by Turbiscan Stability Index(TSl) and EDLVOTheory. The results showed that with the increasing concentration of kaolinite suspension system TSl decreased,showing the stability of system enhanced. By addition of cations,the system TSl increased and instability of system enhanced. Due to the lower energy barierthe more cations concentration was ,the greater system TSl value was,which led to the more instability of the system.The study by additon of diferent kinds of cations showed that with the same ionic strength,the order for effects of instability of suspension was Na+