Abstract: Based on an actual engineering project, to ensure the safety and stability of both the existing station and the undercrossing tunnel section during construction, this study conducted a detailed analysis of the risk factors with the PBA method for closely undercrossing the existing station from three aspects: the construction environment, the construction process, and the operation phase. By systematically identifying risk sources, the study analyzed various risk factors including the impact of groundwater on excavation soil layers and the construction process, the influence of poor soil stability on excavation work, the effect of large excavation cross-sectional spans on the structure of the undercrossing tunnel section and the existing station, as well as the high-standard requirements for controlling settlement of the existing station. In response to different types of the aforementioned risk sources, effective control measures such as wellpoint dewatering, grouting reinforcement, and dual pre-support were summarized and implemented through collective discussions among technical staff, expert analysis and evaluation, and construction process simulation, ensuring the safety and stability of both the existing station and the undercrossing tunnel section during construction. Through systematic risk identification and the application of reasonable control measures, the safety and stability of the existing station and the undercrossing tunnel section were ensured, and references for risk identification and management were also provided for other similar projects.