The current water quality of Luopengwan section cannot reach the standard stably. In order to further improve the success rate of national assessment of water quality andcontinuously improve the water environment quality, the research on Luopengwan section of water quality and water environmental capacity calculation of Xu River was carried out. According to the analysis of present situation of hydrology, water quality and pollution source data, the reasons for exceeding the water quality standard of Luopengwan section were analyzed. We used the control section standard method to calculate the maximum permitted discharge amount into Xu river. The results show that the recent water environmental capacity of COD is 3011.8 t/a, the environmental capacity of NH3-N is 195.0 t/a, and the environmental capacity of TP is 99.2 t/a. The forward water environmental capacity of COD is 1738.7 t/a, the environmental capacity of NH3-N is 135.9 t/a, and the environmental capacity of TP is 70.0 t/a. According to the calculation results of water environmental capacity and the current situation of pollutants into the river, the proportion of pollutants to be reduced is calculated, so as to provide theoretical support for water environment regulation of Xu River.