The water quality data were collected at 11 typical sections in the middle and lower reaches of the Hanjiang River from 2013 to 2020. The single-factor index method, comprehensive pollution index method, and the water pollution index method were used to analyze the variation characteristics and causes of water quality indices at the 11 sections before and after water diversion. The results show that after water diversion, the monthly pollution indices of the 11 typical sections in the middle and lower reaches of the Hanjiang River increased in variant degrees, and the Luohanzha and Xingouzha sections were in the most severe water pollution. The frequency of water quality exceeding standards increased at all sections, with a deteriorated water pollution situation. TN was the dominant pollutant at each monitoring section in the middle and lower reaches of the Hanjiang River. Water pollution related to TP,CODMn and NH3 -N tended to deteriorate from the middle to the lower reaches. Water pollution at the Xinggouzha section was the most severe. In addition to the influence of water diversion, water quality variation was also affected by other factors such as the operation of water conservancy projects, point and non-point source pollution.