In order to investigate the deformation characteristics and load transfer mechanism of deep excavation, a numerical model considering the process of stepped excavating and soil nailing was established by FLAC 3D. The lateral displacement of excavation surface and outside soil, the shear strain increment of soil, and the axial force distribution of nail were analyzed. The results show that, the maximum lateral displacement appears close to slope toe, meanwhile, outside corner is the most disadvantageous location of deflection, and the multilevel platforms have positive effects on controlling soil deformation. Tensile failure and shear failure are the two main failure modes of excavation slope. The location of potential sliding surface can be indicated by shear strain increment contour, and the location moves toward the outside end of soil nail due to soil nail reinforcement effects. The maximum axial force of soil nail appears near the middle and the relative minimum value near the two ends, and the distribution of maximum axial force agrees well with the potential sliding surface.