Abstract: In this paper, 3-D FEM was used to calculate the stresses and de formations in the second cofferdam of Three Gorges project, especially, the stress-strain characteristics of the plasticity concrete seepage prevention wall were discussed, and the safety of the project was evaluated. Three constitutive models were employed to simulate the stress-strain relationships of the filled materials in the cofferdam. The theory that losing of capillary suction in unsaturated soil was used to explain the softening phenomena of soil during its immersing. The calculation results was more reasonable.