A lot of phenomena related to propagating various waves are seen when the high-speed train goes through the tunnel,the gas pipeline is broken due to an accident or the air brake of the wagon operates.For instance,a compression wave generated ahead of a high-speed train entering a tunnel propagates to the tunnel exit and spouts as a micro pressure wave,which causes an exploding sound.In order to estimate the magnitude correctly,the mechanism of the attenuation and distortion of a compression wave propagating along a very long tunnel must be understood and the experimental information on these phenomena is required.An experimental investigation is carried out to clarify the attenuation and distortion of the propagating compression wave in a very long tube.Experimental results show that the strength of a compression wave decreases with distance.The attenuation and distortion of compression waves are affected by the initial waveform of the compression wave and by the unsteady boundary layer induced by the propagating wave.The shape of a compression wave becomes different with the propagating distance;that is,a shock wave appears just head of a wavefront and an overshoot on pressure distribution is observed behind a shock wave due to the transition of the unsteady boundary layer. A lot of phenomena related to propagating various waves are seen when the high-speed train goes through the tunnel, the gas pipeline is broken due to an accident or the air brake of the wagon operates. For instance, a compression wave generated ahead of a high-speed train entering a tunnel propagates to the tunnel exit and spouts as a micro pressure wave, which causes an exploding sound. In order to estimate the magnitude correctly, the mechanism of the attenuation and distortion of a compression wave propagating along a very long tunnel must be understood and the experimental information on these phenomena is required. An experimental investigation is carried out to clarify the attenuation and distortion of the propagating compression wave in a very long tube. Experimental results show that the strength of a compression wave decreases with distance The attenuation and distortion of compression waves are affected by the initial waveform of the compression wave and by the unsteady boundary laye r induced by the propagating wave. The shape of a compression wave becomes different with the propagating distance; that is, a shock wave appears just head of a wavefront and an overshoot on pressure distribution is observed behind a shock wave due to the transition of the unsteady boundary layer.