Abstract: The poor mobility of river channels in plain river network is the main cause of serious water environment pollution. Water diversion is one of the important measures to improve the water environment in plain river network area. In this paper, taking Sanshanwei of Foshan City as an example, a hydrodynamic and water quality coupling model of river network was constructed based on the measured data. The model was verified by 15 days of continuous hydrodynamic and water quality monitoring data. The NSE and RMSE model evaluation indexes were used for model evaluation. Four kinds of gate control methods and seven kinds of landscape water level control were designed based on terrain, tidal law and landscape water level. A total of 28 simulation conditions were used to simulate and analyze the improvement of hydrodynamic water quality and the change of tidal level of inner and outer rivers under different conditions, the comprehensive response mechanism of water diversion and drainage flow and its spatial distribution, gate control mode and landscape water level. The results show that the model is reasonable and reliable. The study area is affected by the drainage path, and the difference of river flow is significant. Considering the effect of river flow distribution, water flow path, diversion effect of bifurcated river channel and pollutant concentration of outer river on river water quality, and effectively combining the dynamic water environment capacity of tidal river network and the spatial and temporal distribution of pollution source discharge, the improvement effect of water environment will be very significant. Compared with the low landscape control water level, the dynamic water environment capacity of inner river with high landscape control water level is relatively increased, and the pollutant concentration is relatively low. The diversion flow of different diversion paths increased by 28.00-64.70 % when the landscape control water level increased from 0.2 to 0.8 m. The ammonia nitrogen concentration in the section was reduced by 0.85-5.50 mg/L, and the reduction ratio reached 28.89-67.23 %. This study provides a new idea for the optimization of water environment in plain tidal river network, and provides an important reference value for the relevant departments to improve the water environment of plain river network.