As well known, foundation pit excavation influences the stress and deformation of adjacent soil, and thus existing tunnel. However, the behavior on the deformation of a twin-track tunnel subjected to adjacent excavation is not clear. In order to investigate this behavior, a series of numerical simulations using PLAXIS are conducted in this study. The result shows that the displacement and internal forces near the foundation pit is almost double those far away. Moreover, as the depth of excavation reaches the burial depth of tunnel, the value of displacement of tunnel begins to increase markedly.