Impulse waves are weak-strength pressure waves, which are discharged at the exit of a train tunnel when a high-speed train is entering the train tunnel. Impulse waves acting as sound noises make seriously environmental problems on local residents as well as the biosphere. In order to efficiently control the impulse wave at the exit of a train tunnel, numerical simulations on investigating the generation and propagation of the impulse wave were carried out. A 2-D axisymmetric model train tunnel was simulated at different operating conditions. Different pressure gradients across compression waves were investigated to check their effects on the generation and propagation of induced impulse waves. Impulse waves locating at the near field, at the far field and at locations with different angles of a specific radius were investigated in details. In addition, open-end correction affecting the magnitudes of impulse waves at different locations was discussed as well. The generation and characteristics of impulse waves at different operating conditions were obtained in details in present numerical studies.