Based on Mohr-Coulomb rule about ideal elasto-plastic constitutive model and rock and soil mechanics theory,the simulation on the excavation process of foundation pit reinforced with soil nail was carried out by using the numerical simulation technique of fast Lagrangian analysis of continua(FLAC3D),which considering the reinforcement effect of soil nail and the interaction between soil and soil nail.The soil constitutive law which can reflect the excavation characteristics of soil,the process of excavation and reinforcement simulation,and the double-spring elements used to simulate soil nail are chosen to establish a numerical calculation model.By calculating,the working principle,strain and stress performances of soil nail,as well as the mechanical and deformation responses of foundation pit are analyzed.The results of analysis show that,(1) the fourth and fifth excavation steps make the largest disturbance to the soil;(2) the incremental gradient of shear strain near slip plane is larger than that of other areas,with the reinforcement of soil nails the soil mass in the length of soil nails has become a whole;(3) the axial stress distribution of along the length of soil nail is asymmetrical,the magnitude of stress is larger in the middle of soil nails and is lower at the both ends of soil nails in the upside of foundation pit,but the larger axial stress is at the end of soil nails near the surface of foundation pit,and decreases along the bar of soil nails in the underside of foundation pit.