Accurate forecasting of circulation patterns in the Yangtze River estuary is essential for managing freshwater resources, mitigating saltwater intrusion, and maintaining water quality. This study introduces a forecasting model using the Four-Dimensional Variational (4D-Var) method to simulate estuarine circulation over nearly six months in 2022. The 4D-Var technique optimizes predictions by integrating observational data—such as satellite images and in-situ measurements—into a numerical model, resulting in more precise simulations of tidal currents, salinity, and other key parameters. Our results show that the 4D-Var model significantly outperforms traditional methods in forecasting accuracy, effectively capturing seasonal changes, tidal cycles, and meteorological influences. These enhanced predictions provide critical insights into potential saltwater intrusion scenarios and their impact on freshwater resources.