Abstract: By collecting measured data on water depth, topography, ocean currents, and tide levels in the vicinity of Dingzi Bay, numerical simulation methods were used to study the sedimentary dynamic characteristics of different cross sea schemes in the eastern part of Dingzi Bay, including hydrodynamics, tidal capacity, water exchange, and topographic erosion and deposition, using the Mike21 numerical simulation software. The impact of the cross-sea channel project construction on the sedimentary dynamic environment in the surrounding waters of Lu Island was studied. The results indicate that the construction of the cross sea channel project has significantly reduced the tidal current velocity in the surrounding waters of Lu Island, with a decrease of about 50%; The construction of the project has increased the siltation intensity around Lu Island, with a maximum increase in siltation rate of about 6 cm/a; The construction of the project significantly affects the water exchange around LU Island, resulting in a decrease in water exchange rate. The area with water exchange rate greater than 80% has decreased from 73.1% to 66.9%; the average decrease in tidal capacity during high and low tides exceeds 10%. Overall, the recommended solution（The bridge lengths on the north, middle, and south sides are 100 m, 100 m, and 200 m） that fully utilizes existing waterways is superior to other solutions in terms of hydrodynamics, water exchange, and tidal capacity, with minimal impact on the marine environment. The recommended plan maximizes the coordinated development of engineering construction and marine environment.