With a foundation pit excavation project as the research background, MIDAS/GTS is used for an analysis of the impact mechanism of simultaneous excavation and sequential excavation of double foundation pits on the intermediate buildings. Research shows that compared with simultaneous excavation, the maximum deformation displacement of the foundation pit enclosure structure has been reduced by about 45%, with the settlement displacement of the building raft increased by about 50%~111% compared with that of simultaneous excavation. Based on a data simulation analysis, the most unfavorable positions of two different excavation methods on the building can be identified, with compared differences between the two so as to optimize the construction steps to ensure the safety of the building. The research on the excavation of double foundation pits can provide reference for similar projects.