The interaction between newlybuilt Guantouling Tunnel on WenzhouFuzhou Railway and existing Tongsan Highway Tunnels is studied. The displacement and stress of upper tunnel and lower tunnel are simulated by software ANSYS, and the analytical results are compared with monitoring data. Some conclusions are drawn as follows: 1) The crown top settlement of undercrossing tunnel is small and the horizontal convergence of it is large, the arch waists and sidewalls are weak points should be supported at overlapped section. 2) The settlement of upper tunnel at overlapped section is large; the settlement of inverted arch is the largest, followed by those of sidewalls, arch waists and crown top; the horizontal convergence of tunnel at middle and lower part varies much. 3) The homogeneous variation of stress of covered strata would be induced by construction of underneath crossing tunnel, as a result, torque would be induced.