To achieve the projected goal of extending a 12.5 m deep water channel upward from Taicang to Nantong, a regulation project on the key parts of Tongzhousha shoal is designed to improve its ability of navigation. The regulation project includes the construction of submerged dike and groin. To investigate the function of the groin and provide the scientific basis for its final design, a 2D hydrodynamic numerical model of Tongzhousha shoal reach based on SWEM2D model is established to study the variation of tidal current after completion of the regulation project. The results show that the first five groins at upper stream are mainly to consolidate the shoal as well as stabilize the channel, and the other three groins are mainly to divert the water and deepen the water depth. The regulation project including the submerged dike and groins is mainly to reduce the water distribution at Langshan shoal channel and increase the flow dynamics at the shallow section.