Abstract: Based on water quality monitoring data of Taihu Lake,the trend of annual and yearly variation of water quality and nutrient were analyzed. The results showed that total nitrogen and total phosphorus did not meet the national standard. Nutrition index and total phosphorus reached the peak in the third quarter in 2017,and total nitrogen reached the peak in the second quarter. In recent years,total phosphorus increased gradually and its ecological function regionalization was Class Ⅳ. Total nitrogen fluctuated around a stable value,which was ClassesⅤ,and nutrition indexes were stably light eutrophication.