Abstract: In order to grasp the change trend of surface water quality in Jiaxing City since the "13th Five-Year Plan", the changes of water quality were analyzed from the aspects of the proportion of water quality categories, the concentration of main pollutants,the rate of section exceeding the standard, and the comprehensive pollution index of 21 indicators of each water body based on the monitoring data of 73 municipal control sections in the city in 2016-2020. The results showed that in 2016-2020, the proportion of Class Ⅰ～Ⅲ water quality in the municipal control section of Jiaxing increased by 72.6 percentage points, the annual change rate was 36.7%, and the quality of poor class V decreased by 1.4 percentage points. The improvement rate of Ⅰ～Ⅲ water quality in each region was in the order of Tongxiang>Pinghu>Jiaxing>Haining> Haiyan>Jiashan. The main pollution indicators were improved to varying degrees, among which the concentration of petroleum, ammonia nitrogen and BOD₅ were improved the most, which were 80.0%,47.7% and 31.4%. The concentration of dissolved oxygen, total phosphorus and fluoride improved the least. The total phosphorus was always in the top three of the section exceeding the standard rate. The proportion of class Ⅰ～Ⅲ in 33 water bodies increased from 30.3% to 87.9%, and the comprehensive pollution index of 21 water bodies showed a significant downward trend. The water quality of the sections located in Pinghu, Haining and Tongxiang was similar and the pollution was similar, while Jiashan and Haiyan overall water quality was better.