Rapid urban development in cities often requires construction activities close to existing tunnels， including basement excavation directly above the tunnels. Based on three dimensional finite element method， the influence of basement excavation on the underlying tunnels was studied. In the numerical model， A tunnel was located under a rectangular excavation with its axes parallel to the long side of the rectangle. The results of numerical analyses indicate that for the tunnel located underneath the centerline of the excavation， overlying excavation will cause the shortening of horizontal diameter and the lengthening of vertical diameter of the tunnel lining. For the tunnel located close to the diaphragm wall， maximum diameter changes often take place in a sub-vertical direction due to the rotation of the tunnel lining during excavation. The spatial effect of the excavation also has an obvious influence on the displacement and distortion of the tunnel cross section.