Abstract: The complex pressure field resulted from a high-speed train entering a tunnel was investigated based on the theory of aerodynamic sound. In light of actual conditions, the Ffowcs Williams-Hawkings (FW-H) equation was simplified to save calculation resource and calculation time. The Galilean transformation was applied to the simplified equation to make a surface function related to only coordinates. Then, by applying the Fourier transform the problem was transformed from the time domain into the frequency domain. Finally, the compression wave profile was determined by virtue of solving the Ffowcs Williams-Hawkings equation with the help of the Green function methods, according with the present experimental result.