Three-dimensional time-dependent calculations are performed to investigate the compressible turbulent flow about a train passing through a single-track tunnel. The “snapper” algorithm in KIVA-3 is used to allow the train to pass through the stationary tunnel mesh. Actual train geometry is simplified considerably. The length of the train/tunnel as well as the speed of the train is considered to investigate their effects on the train-tunnel interaction. In an effort to understand the whole process of the train-tunnel aerodynamic interaction, the formation and propagation of the pressure waves, the radiation and reflection of the waves at the tunnel portals and the histories of aerodynamic forces on the train are studied. The experimental results compare well with the computational data.