Development and utilization of urban underground space is conducive to improving the urban functions, giving full play to the city's social, environmental and economic benefits, but also inevitably encounters many new and more complex geotechnical engineering problems. In this paper, we took a foundation project above the metro subway tunnel in Guangzhou as an example, for which a numerical model was established to calculate and analyze the influence of excavation on the existing tunnel from aspects of deformation, additional stress of tunnel segments and anti-floating stability. The results show that the excavation inevitably leads to soil deformation at the bottom of the foundation pit, which causes displacement of the tunnel and change of the stress state of the tunnel segment. The results provide valuable reference to the project design and construction. It is helpful to other similar projects.