With the development of urban construction, excavation of new projects adjacent to metro tunnels will affect soil and existing metro tunnels. Based on a highway construction project collinear with metro tunnels in Shanghai, the impact of different subgrade excavation conditions on tunnels was investigated using the FDM software FLAC 3D. The results show that the vertical deformation of tunnels is less sensitive to the increase in the width of subgrade excavation area, compared to the area length in the longitudinal direction. Doubling the longitudinal length of excavation area will increase vertical displacement of tunnels by 90%, compared with 17% when doubling its width. In the case of excavating simultaneously in two adjacent areas, the additional vertical displacement of tunnels decreases rapidly with the increase of distance between two excavations. When the spacing of two pits is 30m, the extra displacement is less than 13% of a single excavation.