By using numerical analysis methods to simulate the deep excavation, a lot of analyses are established on the basis of two-dimensional plane strain, ignoring the fact that foundation pit possesses three dimensions. For soil constitutive relation, people always take linear and nonlinear model, without considering the plastic behavior of soil. Using plastic-elastic hardeningmodel to simulate constitutive relation of soil characteristics, the authors carried outmechanical analysis for pit excavation and support. The results show that the analysis for the stress state of pile anchor system is an effective waywhich provides theoretical basis for calculation of soil displacement.