Abstract: The river water environmental capacity is a theoretical basis for the implementation of total quantity control on pollutant emission, and it is also a scientific basis for river water environmental management. Using a comprehensive identification index method, water pollution situation of the river and the main pollution indicators were identified, and water quality of different aquatic ecological function regionalizations in the Kou River was assessed. The method on aquatic ecological function regionalization was put forward based on the difference of water ecological system. The variation of river water quality was simulated by a one-dimensional water quality model, and water environmental capacity of COD_Cr and NH₄-N in the Kou River upstream higher aquatic ecological function regionalization, the midstream lower aquatic ecological function regionalization, Nanchengzi higher aquatic ecological function regionalization were calculated combining with a linear programming model. The results show that water environmental capacity of COD_Cr and NH₄-N are 852.22 t·a^-1 and 47.96 t·a^-1 in the Kou River upstream higher aquatic ecological function regionalization, 410.33 t·a^-1 and 23.09 t·a^-1 in the Kou River midstream lower aquatic ecological function regionalization, 25.23 t·a^-1 and 1.58 t·a^-1 in the Nanchengzi higher aquatic ecological function regionalization, respectively.