Abstract: In order to explore the influence of the development of navigation junction on Min River in the upper Yangtze River, Tangba navigation junction was selected as the research object which is one of the second order of Min River navigation junction. Analyzing the inflow load in channelized river sections of the reservoir area in accordance with the monitoring data in 2016. Numerical simulation of changes in water quality under three scenarios including before and after the completion of Tangba and in the case of Class III incoming water were performed using MIKE21 model. Then the changes of the pollution zone after the tributary merges was analyzed and the water environmental capacity was also calculated. The results showed that the current source pollution load of the canalized river section in the reservoir area mainly came from the mainstream of the Min River. After completion of construction of Tangba, the CODcr and NH₃-N concentrations meet the Class III water quality standards, and the TP concentration is worse than Class V in front of the dam. In the case of Class III incoming water, the TP concentration becomes Class V. The areas of the polluted zone formed by the tributary flowing into the channelized river section have changed: NH₃-N in Zhenjiang River and Tongche River not form a pollution zone, and the area of NH₃-N pollution in Taihe River decreases, while others have increased. In front of the dam, water environmental capacity of CODcr was reduced by 3 280 t/a, NH₃-N was reduced by 368 t/a, and TP had no remaining water environmental capacity. In the case of Class III incoming water, the water environment of CODcr and NH3-N was decreased. However, the TP had no remaining water environmental capacity. Water environmental capacity of the three types of water quality factors of Tongche River was increased, while Zhenjiang River decreased. There is no remaining water environment in the Taihe River before and after the dam was constructed. This study can provide a scientific basis for the reduction of pollution sources and the designation of countermeasures in Min River.