Abstract: The influence of the initial static stresses on dynamic responses of tunnels and underground structures is studied.Some disposal methods of the initial static stresses are presented and a preferable method is recommended in the analysis of train vibration responses of tunnels.Dynamic responses of a tunnel due to the train vibration are calculated.Results indicate that the initial condition in dynamic analysis is not only the input Gauss point stresses but also the input nodal loadings,or mistakes will be aroused.In dynamic calculation of anterior time steps,the static residual forces should be only acted.When the system responses incline to static states,the vibration loading is input and the dynamic calculation of remaining time steps is continued.