Abstract: Based on the Soil Nailing Retaining project in the external angle of a foundation pit in Beijing. By using Midas/GTS software, theexcavation model of the foundation pit is established, the redundancy of the support system is calculated by taking soil nail axial force and soil deformation as the standard, and the influence of reinforcement of waist beam and parameters of the external angle on redundancy of the foundation pit support system are analyzed. The results show: ①Compared with the no-waist beam system,displacements of the negative position in the external angle can be controlled positively by the soil nail-waist beam system. Also, the force transmission paths are added and the redundancy is improved. ②By using the soil nail-waist beam system, the axial force of nail near the external angle can be reduced, the dangerous components can be protected and the redundancy of bearing capacity can be also improved. ③The redundancy of supporting system is reduced with the external angle’s protruding length increase and the size of the external angle reduce.