Abstract: Objective To observe the change of microbial indexes caused by the treatment of municipal sewage treatment plant.To explore effects on the environment and the sewage discharge standard.Methods The samples collected from the source of sewage and the treated water at regular location and time were determinated according to the national standard.The monitoring data of physical-chemical indexes were also collected.Results In the treated water,the total count of bacteria was as high as 720 000cfu/L.Both the total coliform and fecal coliform were> 16000/L.The positive rates of enterovirus in the sewage and the treated water were 58.33%,16.67% respectively.Conclusion The improvement on physical-chemical indexes was good.The effect of treatment on bacteria and viruses was unsatisfactory.So the study on discharge standard of the treated water in municipal treatment plant should be strengthened.