Abstract: The monitoring data of Lijiang River from 2015 to 2022 were used to analyze the water quality of the urban section of the river adopting the evaluation method of single factor index, comprehensive pollution index evaluation method, and comprehensive nutritional status index method before and after the dam was constructed. The water qualities of Dongzhen waterworks, Dongjiang waterworks,Wayao waterworks, Mopanshan were examined. The results indicated that the water quality of the Chengbei waterworks, Dongzhen waterworks, Dongjiang waterworks were maintained at class Ⅰ～Ⅱ before the construction of the dam. The water quality of Wayao Water Works and Mopanshan section is maintained at class Ⅱ-Ⅲ as well. After the dam was built, the water quality of the 5 monitoring sections was maintained at class Ⅰ～Ⅱ. The main factors affecting water quality is dissolved oxygen, permanganate index, five-day biochemical oxygen, and total phosphorus. After the dam was built for backwater, the water quality of Wayao water plant and Mopanshan was improved significantly. However, the water quality of the other three waterworks did not change significantly. During January of 2023 to December of 2023, the water quality of 5 monitoring sections was in the state of poor nutrition. No eutrophication was observed.