Drainage problems occurred in Wuhan city in 2016, and the Jiangnan Pump Station was required to be put into use in advance. In order to meet the requirements of the construction period, the original supporting structure of continuous underground-wall plus three inner support must be optimized. In order to clarify validate the feasibility of the new supporting structure, the excavation process of the foundation pit using the original supporting structure and the new supporting structure was simulated, and then the obtained horizontal displacement, bending moment and surface subsidence were compared and analyzed. The test results showed that, the horizontal displacement, bending moment and surface settlement increased to some extent after if the pit support structure change to the form of large diameter cast-in-situ pile plus one inner support, but the stability of the foundation pit can still be ensured. The research results showed that the reduction of the support stiffness and the number of supports have a great impact on the maximum horizontal displacement and surface settlement, and deepen the location where maximum horizontal displacement occurs; however, it will not affect the ground surface subsidence law and the location of the maximum displacement. This research can be used for reference in similar foundation pit engineering.