Abstract: The FLAC^3D software is adopted to simulate and analyze the project based on some unstable and damage phenomena such as fracture of top soils of side slope and collapse of bottom soils of side slope during stagged excavating and construction of soil-nailing wall in a deep foundation pit of the building of Beijing Science Park of China National Nuclear Corporation. In order to ensure the reality of the numerical simulation approach, several factors are considered, in duding distribution of soil layers, gradient of side slope, arrangement pattern of soil nails, reinforced steel shotcrete surface, pore water pressure of aquifer, stagged excavation and support. According to the size of the deep foundation pit, the corresponding three-dimensional model is established. The Mohr-Coulomb elastic-plastic model is used to compute the displacement deformation of side slope at different excavation and support stages, and the displacement deformation nephogram of the whole deep foundation pit and the maximum displacement cross-section are acquired through the post-processing procedure. The horizontal displacement and settlement at several key nodes are recorded. The horizontal displacement and settlement of side slope caused by excavation and support in actual project are measured. The numerical results with are compared the measured data to determine the approximate position of potential sliding surface and collapse in the deep foundation pit. Thus it may offer some important reference for improving supporting pattern for the area with large the displacement in the design.