In order to study the influence of seepage effect on granite residual soil tunnel, seepage is realized by injecting water into surrounding rock, followed by a numerical simulation. In the simulation process, four groups of water pressures (0, 50, 100 and 150 kPa) have been set up, thus obtaining the relationship between different pressures, displacements and supporting structures. The results show that, with the pore water pressure of surrounding rock being 50 kPa, the excavation of the upper step is unfavorable; with the pore water pressure of surrounding rock being 100 kPa, the excavation of the lower step is more unfavorable. Tunnel excavation is greatly influenced by water pressure. The larger the water pressure is, the wider the seepage range is, and the more serious the inverted arch uplift will be. At this time, the top lining structure is characterized with a large deformation, which makes the supporting and monitoring of the tunnel excavation quite necessary. After supporting the upper steps, a timely supporting should be given to the surrounding rock so as to avoid a large displacement caused by excessive seepage. The construction of the lower steps of the tunnel is influenced by multiple factors, and the vault should be reinforced in time to avoid unnecessary engineering accidents.