With the surge in the "double-carbon" mandate within geotechnical engineering, there's a notable rise in eco-conscious underground construction technologies. Among these, the bottom-expanding load-bearing steel pipe concrete inclined support stands out as a novel foundation pit excavation support system. Multiple engineering cases affirm the efficacy of this inclined support system, yet its operational mechanism warrants deeper exploration. Employing finite element numerical simulation, this study delves into the deformation traits of such bottom-spreading inclined braces within real pit excavation projects. It scrutinizes the impact of soil stiffness and the inclined brace's angle on support efficacy. Results indicate that the extended bottom inclined brace significantly controls soil deformation during foundation pit excavation, particularly in softer soil regions. An increased inclined angle enhances lateral force support, augmenting bearing capacity. This proves instrumental in restraining soil and retaining wall deformation. However, it comes at a heightened project cost, demanding careful selection contingent on specific engineering conditions.