Based on different characteristics of pure-cultured Microcystis aeruginosa in different growth phases,the effect of potassium permanganate pre-oxidation,on the DOC of intracellular and extracellular,removal efficiency and changes of cells were studied,and PAC was used as coagulant for subsequent coagulation.The results showed Low concentration potassium permanganate used in pre-oxidation phase can inhibit the algal photosynthesis,and high concentration used would inactivate the algal cells and release large quantities of intracellular organic matter.When potassium permanganate dosage is 2mg/L and PAC dosage is 30mg/L,in 9d、21d、28d、36d,the removal rates of algae are 81%、99%、58.2%、35.35% respectively.In different potassium permanganate dosages,algal samples reach the best removal efficiency in 21day which is the logarithmic stage,which may be related to the content and components of Extracellular Organic Matter (EOM) in different growth phase.In early senescence phase and late senescence phase,the concentration of EOM significantly increase,which affected oxidation of potassium permanganate and thus resulted in the decrease of coagulation effectiveness.Since the concentration of EOM was low in stationary phase and logarithmic phase,oxidant could contact with algae and promoted algae to secrete EOM.The proper amount of EOM can enhance the efficiency of algae removal.The reduction product of potassium permanganate is hydrated MnO₂,which will promote coagulation and can be attached to the surface of algae to improve algal cell sedimentation.