Comparison of the treatment effect and mechanisms of different preoxidants on algal cells were analyzed by the experiments of inactivation of M. aeruginosa with potassium permanganate, ozone and sodium hypochlorite. The results showed that the decrease of quantum yield of M. aeruginosa caused by chlorination and ozonation both followed second-order kinetics. Sodium hypochlorite caused the cell lysis with the quantum yield rate constant of (220±3) L·mol-1·s-1 and resulted in the release of intracellular organic matter(IOM) regardless of initial concentration. Ozone had a profound oxidation effect on M. aeruginosa cells and would rapidly cause the cell lysis with the rate constant of (2 655±15) L·mol-1·s-1regardless of the initial ozone dosages. The sequence of the quantum yield rate constants of three oxidations was O₃>NaClO>KMnO₄. However, both ozone and sodium hypochlorite caused the cell lysis and led to the release of IOM more easily than potassium permanganate, which was suggested by the results of scanning electron microscopy.