To further understand the aerodynamic effects and the characteristics of train wind, the RNG κ-ε model was used to simulate the overall process of a high-speed train passing through a tunnel asymmetrically. The movement of the train was simulated using the sliding mesh technique. The aerodynamic effects and the train wind characteristics were investigated, and the accuracy of the numerical method was verified by comparing the numerical results with the results of a full-scale experiment. Results show that there was a large difference of pressure transients between the entrance and inside of the tunnel. The maximum positive pressures and the peak-peak pressure transients amplitude differed by 13.1% and 7.3% at the symmetrical monitoring points on both sides of the train. The longitudinal velocity component and the maximum resultant velocity on the near-tunnel side were 2.1 and 1.9 times those of the far-tunnel side respectively. The train passing asymmetrically had no obvious effect on the aerodynamic pressure, but the impact on the train wind was significant. The boundary layer of the train had a significant effect on the longitudinal component of the train wind, while the effect on the lateral velocity component and the vertical velocity component was small. Complex wake vortex structures alternately appeared behind the tail, which was very different in the open air. The attenuation of the train wind velocity in the tunnel was slower, and the duration was longer.