In order to accurately measure the influence of operation mode of Qipu River water diversion project for Yangcheng Lake and the surrounding river networks, 7 numerical experiments were designed based on Taihu water quality and quatity model. The influence is evaluated from two aspects of diversion volume and rainfall type, and the overall water quality compliance rate of river network is defined as the evaluation criteria. The results show that the water concentrated to the northern and southern rivers, and the water qulity of west part of Yangcheng Lake improved while the middle and eastern part deteriorated, it was also revealed that the best improvement of water quality happened when the water diversion volume ranged between 20~40 m³/s. The effect of water diversion on the water quality of the river network has a significant spatial difference. In different rainfall conditions, water quality of river networks and lake can be improved by the water diversion scheduling to a certain extent.