Transient pressure variation generated by two trains passing through a tunnel has great influence on train safety and passenger comfort. Therefore, research on this area is particularly important. The model of 350km / h EMU of three cars passing each other through a 300m tunnel with constant velocity was built, based on three-dimensional unsteady Navier-Stokes equation of compressible viscous fluid and RNG
turbulent model. This process was calculated numerically by means of finite volume method, pressure and aerodynamic forces of train, while pressure variation of tunnel was studied in this article. The results show that pressure variation of different points is similar for the identical side of the train, and pressure variation of the middle tunnel is most violent when the EMU are passing each other here; compared with single one. The pressure amplitude of train crossing each other in a tunnel is twice more, head of the train get the highest value with 177.3% bigger, while the pressure amplitude of the middle tunnel is twice as single one approximately; besides, the air resistance and side force are larger, while the lift force is minor relatively, the max drag coefficient is 1.340, the max lateral force coefficient is 0.567, and the max negative lift coefficient is -0.190; in terms of different cars, the middle one comes in for the smallest force of all, while drag force amplitude of the head and middle car are 136.3%, 20.7% larger than the middle one separately, lift force amplitude are 76.1%, 79.5% larger and lateral force amplitude are 38.8%, 24.2% larger separately.