Based on the Reynolds time-averaged equation of three-dimensional

unsteady and compressible flow and the standard k-ε two-equation turbulence model

the transient pressure change of a two-speed 400 km electric multiple unit (EMU) train during the most unfavorable rendezvous in the center of a tunnel is studied with the sliding grid technique. The results show that with the increase of the longitudinal length of the train

the positive peak value and the peak to peak value of the transient pressure on the train surface decrease

while the negative peak value remains basically unchanged. When the tunnel wall pressure is in the range of 0 and 160 m from the tunnel entrance

the amplitude of the tunnel wall pressure increases slowly with the increase of the distance from the tunnel entrance but rapidly in the range of 160 m and 324.5 m and reaches the maximum 16 460.74 Pa at 324.5 m. Then it decreases rapidly in the range of 324.5 and 520 m but slowly to 3 740.33 Pa in the range of 520 m and 649.5 m. The maximum difference between the maximum and minimum values of pressure change is 340.1%.