Abstract: With the hydrological and topographic data from sea area near Yulong Island, Shandong, the sedimentary dynamic patterns of current, erosion and deposition, water exchange rate before and after the cross-river engineering (bridges or tunnels) were simulated numerically, and the impact of the engineering on the internal sedimentary dynamic environment of the Yulong Island was discussed. Results show that the engineering would decrease the tidal current velocity in overall, and the maximum reduction is over 20 cm/s. This situation would weaken the hydrodynamic environment such as the erosion and deposition in waterways, and change the micro erosion environment. In some regions, siltation would occur and the maximum annual siltation is over 2cm. In addition, the project will influence the water exchange within waterway. The rate of water exchange would be reduced by less than 60% locally. As a whole, it is suggested to build bridges across Jingyi River and Jinger River, while to use pipe and culvert in Weiyi River would be the best option with a minimal impact, which accords with the actual requirements of engineering construction. Coastal engineering construction should prioritize marine environmental protection and achieve coordinated development between engineering and the environment.