The finite difference model of FLAC3D was used to simulate the construction process of prestressed anchor composite soil nailing excavation dynamically,and then the deformation of soil in the process of foundation pit excavation was analyzed.The results show that the horizontal displacement of soil increases with the depth of excavation,and the inclination of soil mass to the pit is restricted as the result of the entrance of the anchor.The horizontal displacement curve of pit was "bulging",and the simulation and measured values are much closed with only 0.75 mm.