Abstract: To study the characteristics of water environment changes in different tail water receiving rivers, 33 samples were collected from 4 groups of the rivers, and five indicators, COD_Mn, TN, TP, NH₃-N and Chl-a, were determined. Combined with high-throughput sequencing, the water quality changes, eutrophication characteristics and bacterial community structure were analyzed along the distance. Results showed that:the change of pollutant concentration caused by tailwater would recover to background value within 50~100 m except TN. The supplement of tailwater increased the bacterial richness and diversity, but the proportion of dominant species decreased and their relative abundance changed. After 50~100 m, the proportion began to increase and Proteobacteria became the absolute dominant phylum. At the level of genus, the relative abundance of dominant bacteria in background section all decreased with supplement of tailwater, while the abundance of Rhodovulum, Pseudoalteromonas, Massilia were significantly negative correlated to river eutrophication index (P<0.05). When the discharge ratio was ≥ 50%, the similarity of bacterial community structure between downstream and tailwater outlet was higher. In addition, tailwater may bring a large number of other microbial species, causing an increase in ecological risk of river.