The natural river water quality model is usually not applicable in city rivers under high strength human activities; and the water quality model coupling human activities such as water structures is necessary for simulation of the water quality in rivers under the both natural and human activity conditions. In this paper, a water quality model coupling water cycling, water diversion and circulation line engineering with the natural processes was developed to describe the complex water quality processes based on the Distributed Time Variant Gain Model (DTVGM) and one-dimensional stable-state model, which can be used under different scenarios both in the past and future. The results show that the model performs well in the basin. Furthermore, the model was used to analyze the influence of different scenarios of water diversion on the water quality in the river reach. The results also show that the water quality will be improved after the first and second diversion projects, which can provide certain scientific basis for the protection of the water ecological environment in the basin.