In order to improve the water environment of the main urban area of Changzhou City, through the combination of numerical simulation calculation and field test, the research on the scheme of improving the water environment of smooth flowing water was carried out. Using high-quality and abundant water from the Yangtze River as the water diversion source, the Weicun water conservancy project and the Zaogang water conservancy project were used to divert water. Five groups of simulation schemes were set for the new project of Daxi project of the Dayun River and the dispatching combination with four movable weir projects. Through the hydrodynamic mathematical model, the flow distribution of the river in the urban area under each scheme was simulated. Based on the field test, the effect of the recommended scheme was demonstrated. The results show that the recommended scheme has formed a smooth flow pattern of three-level water level difference, accurate water level regulation and reasonable flow distribution, and the water environment of the river network has improved significantly. At the same time, most of the water quality indicators are still in a good state within 16 days after the end of water diversion, but the water quality of some rivers has rebounded significantly. It is an effective way to improve the water environment of plain river network cities to carry out hydrodynamic regulation through the mathematical model. However, it is necessary to strengthen daily monitoring, reasonably determine the living water cycle according to the water quality changes, and carry out pollution source analysis for some abnormal water quality points, so as to ensure the long-term treatment of river network water environment.