Taking the deep foundation pit of an internal support system in soft soil area as the research background, The actual project merges the foundation pits of the original plan and adjusts the horizontal and vertical arrangement of the support. In order to study the optimized effect of the scheme adjustment, the original scheme and the optimization scheme model were established by using the numerical simulation software PLAXIS. Firstly, the validity of the numerical simulation was proved by comparing the calculation results of the optimization scheme with the engineering data, and then the original scheme and optimization scheme were compared. The results of the comparison show that the optimization scheme is better than the original scheme for the deformation of the soil outside the pit and the deformation of retaining structure. Finally, the cost and construction period of the two schemes are compared. The results show that the optimization scheme has lower cost and shorter construction period. Therefore, the effect of this optimization is obvious. The optimization method and the conclusions obtained can provide reference for similar projects.