The excavation of a deep foundation pit is often required for the reconstruction of urban road underpasses, and deep foundation pit excavation has obvious spatial effect. In order to gain an in-depth understanding of the spatial impact of deep excavation on the enclosure structure and the surrounding environment, the on-site monitoring and numerical simulation studies based on the deep foundation pit project of the K2+000~K2+120 section of the Shenzhen Gongchang Road underpass reconstruction project were carried out. Numerical software Midas GTS was used to investigate the effects of overloading, enclosure pile diameter and steel support preloading on stress and deformation of deep foundation pit enclosure structure through parametric analysis. The results shows that overload around the perimeters of the pits deformed the perimeters and caused significant settlement of the surrounding ground. The spatial effects of pit stress, deformation and settlement of the surrounding ground surface were affected by changes in peripheral overload. When the diameter of fender pile was greater than 0.8m, its spatial effect on the bending moment of the surrounding structure was of great importance. By applying a pre-stressing force to the steel support, the bending moment of the enclosure structure could be adjusted to reduce pile displacement and control the value of the surrounding surface settlement. For this project, the prestressing force of the steel columns did not have a significant effect on the spatial effect of the pit. The study could serve as a reference for designing and constructing similar pits in other areas.