A study was made of the effect of ultraviolet rays(UV)irradiation on the inactivation and photosynthetic activity of microcystic aeruginosa,and an investigation was made into the change of water quality in the algae solution.Results show that the inactivating efficiency increases with the increasing of UV fluence,but the photosynthetic activity decreases exponentially with the increasing of UV fluence.Under the algae concentration of 35×108(cell)·L-1,the algae is suppressed effectively at the UV fluence of 91.8 mJ·cm-2.The corresponding optimum irradiation duration is 10 min.The concentration of microcystic aeruginosa determines its inactivation,and the removal efficiency of the algae with high concentration is more obvious.UV radiation is less influential on the UV254 of algae solution.With the increasing of UV radiation intensity,the removal of DOC presents an initial increase and then a decrease.