In this paper, compression waves produced by trains which enter a tunnel at high speed were numerically investigated. The equations of the one-dimensional, unsteady and compressible flow in which the area of a tube is dependent on the time and the distance were numerically solved by the method of characteristics. The calculations were performed for trains with various speeds, nose lengths and cross-sectional area ratios, and the effects of these parameters for the shape and the strength of compression waves were quantitatively crarified. The results show that the pressure gradient of compression waves is affected largely by all of these parameters.