The passenger comfortability induced by the pressure waves generated by the passage of highspeed trains in a tunnel is a matter of concern. The singletrain waves and trainmeeting waves can be calculated using the onedimensional unsteady compressible flow model and the method of characteristics. The trainwall friction, the threedimensional flow of nose and tail of the train in the tunnel and the port flow of the tunnel are all expressed by the empirical coefficients, which are important for the calculation of the pressure waves in the tunnel. The onedimensional uncompressible flow theory is used to establish the computation procedure in this paper. The results show that the computation procedure is effective in comparison with foreign test data.