Abstract: For a plate bracing project of excavation with inner support structure in deep saturated soft clay by adopting the hyperbolic hardening model for foundation soils, the Mohr-Coulomb model for the soils in passive zone and the elastic model for vertical support piles, the influences of the depth and width of reinforcement soils in the passive zone on the support structure are calculated and analyzed. The results show that for the passive zone there is a reasonable reinforcement depth and width. From the control of the internal force, bending moment and shear of the support wall, the reasonable reinforcement depth is about 0.55 times the excavation depth, and the reasonable reinforcement width is 0.36 times the depth of excavation. From the control of the horizontal displacement of excavation and the vertical displacement of the soils behind it, the reasonable reinforcement depth is 0.55 times the excavation depth, but the reasonable reinforcement width is 0.45 times the excavation depth.