Abstract: The sheet-pile structure is extensively used in deep excavations and wharfs as the retaining structure. The key issue is the forces acting on the sheet piles as well as their deformations under the earth pressure. However, the deformations closely relate to the earth pressure. This issue becomes a typical problem of soil-structure interaction. Based on FEM numerical simulations, the working mechanism of the sheet-pile structure is investigated. The following aspects are studied with regard to a wharf case during its excavation: distribution of earth pressures at both sides of the front wall; internal forces and deformation of the structure, stress-strain relationship of foundation soils and rotation of the principal stresses. The results show that accurate modeling of stress-strain relationship of soils is the key to this kind of problem. During the excavation of the harbor basin, the seaward earth pressure of the front wall develops towards the active direction, while the landward one develops towards the passive direction. The excavation induces the rotation of the direction of the principal stress of soils, especially that of the soils under the harbor basin at the seaward side of the front wall.