It is important to reasonably determine the maximum burial depth for the design of the underwater tunnel project in the lower reaches of the Yangtze River. Taking the second tunnel project of Jiangyin as an example，this paper analyzes the characteristics of riverbed evolution and water and sediment movement of the project reach in recent years and determines the typical water and sediment control conditions for model tests from the point of view of engineering safety. The paper uses the physical model test to predict the maximum scouring depth of the riverbed near the second tunnel project of Jiangyin and compare the results with those calculated by the mathematical model. The results indicate that the research results of the physical model and mathematical model are consistent. Under different hydrological conditions，the riverbed is generally scoured. The maximum scour of the secondary channel of Jiangyin on the left side occurs on the right side of the deep channel，and the maximum scour of the main channel on the right side occurs on the left side of the deep channel.