We describe three-dimensional analysis of compressive fluid and three-dimensional scale tests to evaluate and verify the pressure gradient of compression waves that are generated when high-speed trains enter tunnels. We introduce an unstructured mesh and a total variation diminishing (TVD) method to improve the accuracy of calculations. A 1/30 scaled model was adopted in both the calculations and experiment. The traveling velocities of the train model ranged between 270 and 320 km/h. The pressure changes in the tunnel during the experiment were measured to verify the calculation results. The experimental results and calculations agreed well with an accuracy of approximately 10% in both cases with and without a portal hood. We also confirmed that the installation of a portal hood reduced the pressure gradient by approximately 35% because of the increased duration of elevated pressure.