The deformations of an existing tunnel induced by the adjacent double foundation pit excavation at different construction stages were analyzed by establishing a 3D finite element model.The results show that the deformation of the tunnel is great when the double foundation pit is parallel to the adjacent tunnel,and the maximum horizontal displacement is approximately 10% larger than the displacement when the double foundation pit is perpendicular to the tunnel.The later pit excavated later will cause larger deformation of the tunnel than that excavated earlier by about 7%.The excavation of the pit far from the tunnel has few influences on the deformation of the tunnel when the double foundation pit is perpendicular to the adjacent tunnel.The tunnel deformation is mainly determined by the excavation of the foundation pit near the tunnel.No matter which kind of layout,it is found that the excavation of double foundation pit on one side of the tunnel causes superior influence on the horizontal displacement and little influence on the vertical direction of the tunnel.The vertical displacement is about 1/10 of the horizontal displacement.The vertical deformation of the tunnel is an extrusion from two sides to the center of the tunnel.The horizontal displacement of the tunnel is pointed to the side of pit and the horizontal deformation of the tunnel is a tension from center to the edge sides of the tunnel.The most obvious displacement and deformation of the tunnel appear at the place corresponding to the center of the excavated pit.