The　portal　section　of　mountain　tunnels　was　simplified　into　a　slope　with　single　free　face　based　on　the　theory　of　elastic　wave.　The　effect　of　wave　reflection　was　considered　to　deduce　the　solution　of　free　field　ground　motion　on　the　axis　of　tunnel　under　incident　SH　wave.　The　3D　shell　theory　was　employed　to　provide　earthquake-　induced　strains.　Shaking　table　tests　were　conducted　for　the　portal　section　of　tunnel　to　validate　the　theoretical　solution.　The　dynamic　response　of　lining　was　regarded　as　the　superposition　of　the　ones　in　cross　section　and　in　axial　direction.　The　shearing　deformation　occurs　in　the　cross　section　of　tunnel　under　action　of　SH　wave　propagating　parallel　to　the　cross　section.　The　arch　spandrel　and　arch　springing　can　be　seen　as　the　weak　parts　in　seismic　design　of　lining　structure.　As　the　distance　to　the　tunnel　portal　increases,　the　deformation　effect　increases　slightly.　The　shearing　deformation　occurs　in　longitudinal　direction　under　the　action　of　SH　wave　propagating　parallel　to　the　axial　direction　of　tunnel.　The　deformation　effect　is　gradually　weakened.　The　dislocation　occurs　easily　at　the　position　of　construction　joint　of　tunnel　portal　due　to　longitudinal　SH　wave.　Therefore　the　seismic　design　in　longitudinal　direction　of　tunnel　is　also　worthy　of　consideration.　©,　2015,　Academia　Sinica.　All　right　reserved.