Abstract: When a high-speed train enters a tunnel, an initial compression wave occurs and radiates to the outside of the tunnel to form a micro pressure wave when it propagates longitudinally along the tunnel to the exit. An experimental device for generating the initial compression wave by the instantaneous release of high-pressure air was built, and the experimental research on the compression wave generated by it was carried out. Firstly, the composition of the experimental device was introduced, and the pressure time history curve and formation mechanism in the tunnel were analyzed. Secondly, the influence of the parameters of the experimental device on the initial compression wave was drawn out. The subsequent attenuation process of the compression wave was studied at last. The experimental results show that the pressure fluctuation in the tunnel is mainly affected by the reflected wave at the tunnel portal. The amplitude, gradient and positive peak value of the initial compression wave can be adjusted by changing the relevant parameters of the experimental device. The attenuation period of the compression wave is the same under different initial pressures of the high-pressure chamber, but the larger the initial amplitude is, the faster the pressure decays in the same time period.