A zone of highly compressed air moves with a high speed train just in front of the train’s nose on the plain. When the high speed train enters a tunnel, the compressed air zone changes into a compression wave in the tunnel by the piston effect of the train, and propagates in the tunnel at a sonic speed. When it reaches the tunnel exit, an impulse wave is emitted from the exit to the outside. The impulse wave emitted from the tunnel exit generates impact noise and low frequency vibration, and causes serious environmental problems such as affecting private houses and building around the tunnel. In order to solve these engineering problems, it is important to develop the methods to predict the emission pattern of impulse wave emitted from the tunnel exit and to reduce the impulse wave. In this study, the effect of topographical conditions on the impulse wave emission from the tunnel exit was investigated using a new effective emission angle model. The maximum rate of change of compression wave and the peak of impulse wave used in the model were obtained by 3D unsteady calculations using a commercial code.