Abstract: To solve the flood control problem during the construction period of the sea gate in the plain tidal river network area,taking the renovation and expansion project of Nanzhugang South Gate Station in Fengxian District, Shanghai as an example, this study investigates the flood control plan during the construction period of the sea gate under the influence of tidal uplift at both ends. A hydrological mathematical model was constructed by coupling the MIKE11 HD hydrodynamic model with the NAM model, and the model was calibrated and validated based on measured flood data. Based on the 50 year design rainfall and extreme tidal boundary conditions of two typhoons, a comprehensive construction flood control strategy of "diversion channel+water level pre drop+water system connection" was proposed, and 10 schemes were compared and analyzed. The simulation results show that:(1) In the case of a once-in-50-year rainfall, the closure of the South Gate of Nanzhu Port will cause the water level of rivers such as Nanzhu Port and Beigang to exceed the design high water level(3.75 m), with a maximum water level rise of 0.49 m;(2) Scheme Ⅲ-9 constructs a flood discharge channel by setting a diversion channel with a bottom width of 3 m and an estuary width of 3 m, combined with dynamic water level regulation and water system connectivity measures, which can comprehensively eliminate sections with water levels higher than the design high water level of 3.75 m, and the peak water level can drop by up to 0.21 m, effectively reducing the flood risk in the study area while reducing the amount of open channel construction. Research has shown that optimizing the size of the diversion channel and supplementing it with water system regulation can effectively ensure flood control safety during the construction period of the sea gate under the premise of economic feasibility.