Abstract: During the renovation of the old sluice gate, the regional drainage capacity will be reduced. This study takes the renovation project of the South Sluice Gate on Nanzhu Port as an example and uses a one-dimensional river network hydrodynamic model to analyze the impact of the sluice gate reconstruction on flood control in the Fengxian area. The results show that the drainage capacity of the temporary pumping stations during the construction period is lower than that of the original sluice gate. Although some floodwater can be discharged into Hangzhou Bay through surrounding sluice gates, the overall regional drainage capacity is reduced. During heavy rainfall, the water level of inland rivers in Fengxian District rises, showing a distribution pattern of higher levels in the west and lower levels in the east. The maximum water level rise in the rivers near the project site is approximately 0.06 meters. It is recommended to deploy additional temporary drainage equipment, such as mobile pump trucks, during heavy rainfall to ensure flood control safety in the surrounding areas during the construction period.