Foundation pit corner of composite soil nailed wall has obvious spatial effect. Supporting structure near foundation pit corner is safer due to smaller stress and deformation, Whilst at present quantitative beneficial affected area of foundation pit corner to the supporting structure are not known and designs are the same in the middle and the corner of foundation pit. In order to reduce the material consumption and avoid overcautious design, the construction process of excavation and supporting of the composite soil nailed wall of soil nailing and cement-soil piles for deep foundation excavation was simulated through establishing a whole three-dimensional finite element model,which includes the corner of the foundation pit and can consider spatial effect of corner location and the interaction between soil nailing,cement-soil piles and soil through establishing interface elements. Beneficial affected area of foundation pit corner to stress and deformation of the supporting structure is analyzed and quantified. The calculation results show that beneficial affected area of foundation pit corner to the horizontal displacement of excavation face, the subsidence displacement of the ground beside the foundation pit,the bottom heave displacement and the axial forces of soil nails are about 1.3 times, 1 times, 1 times, 1.2 times of the excavation depth. Whole three-dimensional finite element calculation results are basically consistent with those of the field test data and are more reliable than two-dimensional or local three-dimensional. These conclusions can provide theory basis and research method for optimization design and safety construction of composite soil nailed wall.