Abstract: The plain river network area has a flat terrain and slow flow velocity, resulting in a limited ability to resist pollution. Therefore, enhancing the connectivity of the water system is crucial for improving the quality of the water environment. This article focuses on the Yuejin polders which has poor water system connectivity in Shengze Town as the subject of research. By conducting water diversion experiments and constructing a hydrodynamic model of the river network in the polders area, the study explores the scheduling and operation rules of water conservancy work, methods of connecting the river network, and the corresponding changes in the water environment. The study utilizes water age as a time scale parameter to measure the connectivity of the water system. It establishes a river network model for hydrodynamics, water quality, and water age in the Yuejin polders. The simulation evaluates the connectivity and water quality improvement in the polders area under five water diversion schemes. Additionally, an evaluation system of pressure, state and response is constructed to quantitatively analyze changes in water system connectivity and the level of water environmental improvement resulting from water diversion. The results reveal that from the perspective of the length of water exchange, the exchange time of water bodies in the main river channels of the research area is within 5 days. The greater the connectivity of these water bodies, the shorter the water age becomes. From the perspective of changes in water quality indicators, during the water diversion experiment, the most noticeable change in the water environment inside the polders is the level of ammonia nitrogen. It shows a strong response to water diversion, and simulation results indicate that water age generally aligns with the concentration of ammonia nitrogen. Enhanced connectivity of water bodies leads to a shorter water age, which aids in reducing ammonia nitrogen levels. From the perspective of water diversion scheme, the uni-source water diversion and uni-region drainage scheme has limited effectiveness in improving the connectivity of the water system within polders, especially in areas with weak water flow in the river network. This scheme also increases variations in water flow within the polders, resulting in spatial differences in connectivity and water quality in the river network. Consequently, local stagnant water areas or dead water areas may be formed. Therefore, the combination of multiple sources of water diversion and multi-regional drainage scheme can enhance the connectivity of the water system and improve water environmental quality.