Based on the phase II project of Block 07, District 14 of Shanggang, Baoshan New City SB-A-4, Shanghai, the underground three-layer foundation pits were excavated to the basement at one time. Due to project needs, the backfill construction progress of specific super high-rise building areas needed to be excavated sig-nificantly in advance. The calculation method of an elastic ground slab combined with a space frame beam was used to establish an integrated coupling analysis model for the foundation pit and the main structure in the incomplete state and to calculate the interaction mechanism and load distribution between the foun-dation pit and the main structure under a specific state. Under the premise of non-zoned excavation of the foundation pit, the preliminary removal of the supports in the specific area and the backfill construction of the main structure were achieved. The actual measurement data verify that, as a type of strut structure with a large bearing capacity and high structural stiffness, a plate wall combined with prestressed steel diagonal braces can ensure that the plate wall has better lateral stiffness and overturning resistance through the application of matching prestresses. This meets the conditions of an interstage support replacement system for deep foundation pits. The successful implementation of the project provides certain reference value for deep foundation pits that need backfill construction in advance.