Abstract: The Yangshan deepwater port project is the first port constructed along a reef island in the open sea in the world. The large-diameter sand piles are also firstly used in the Yangshan deepwater project to reinforce the soft silt foundation of the shore connecting structure in the deep water of the open sea. In this paper, in order to understand the bearing capacity of the sand piles and the connecting structure, a 3D finite element model is developed to numerically simulate different construction conditions of the sand pile foundation stabilization based on realistic geologic conditions. The reinforcing mechanism of the sand piles is studied to optimize the large-diameter sand pile′s reinforcing area， reinforcing depth and replacement ratio by the force and deformation characteristics of the shore connecting structure and the settlement and deformation behaviors of the soil layers in different sand column reinforcement plans. The research results provide a scientific basis and technical guidance for the optimization of construction in the similar projects in the open sea in the future.