Abstract: A numerical integration of N-S equations was presented for three-dimensional unsteady viscous compressible isentropic flow to study the compression wave induced by the high-speed train entering into underground Sanchakou station.Result shows that the maximum pressure wave at the same measure point in the double track tunnel when the high-speed train running from double track tunnel to single track tunnel is bigger than that when the high-speed train running from single track tunnel to double track tunnel,while the maximum pressure wave at the same measure point in the single track tunnel when the high-speed train running from double track tunnel to single track tunnel is smaller than that when the high-speed train running from single track tunnel to double track tunnel.The more the cross-sectional area of tunnel,the smaller the pressure wave is regardless of the high-speed train running towards.The maximum pressure wave value at the measure point in the transition section tunnel is obviously bigger when the high speed train passing through in the middle of the transition section tunnel than that when a single high-speed train running through the transition section tunnel and it is no more than two times.