Abstract: Using FEM and a mathematical model based on the concept of inertial force, a program for the 3 D analysis of the seismic responses of tunnel is compiled. Then, 3 D seismic responses for the portal section of a tunnel is analysed by means of FEM. In the analysis, four types of boundary conditions, excitation in three different directions, two groups of damping coefficients of the surrounding rock mass, three different widths of the finite element mesh and the effect of anti sesmic joints of tunnel structure are discussed.