Evaluating　the　impact　of　the　isolation　layer　on　the　tunnel　＇　s　response　is　crucial　in　the　practical　engineering.　An　analytical　solution　for　the　longitudinal　seismic　response　of　a　tunnel　covered　by　an　isolation　layer　is　first　proposed　in　this　study　based　on　an　improved　elastic　foundation　beam　model.　Wherein,　an　equivalent　beam　model　for　the　tunnel　-isolation　layer　system　is　built.　The　tangential　interaction　effect　at　the　ground　-isolation　layer　-tunnel　interfaces　is　taken　into　account　by　solving　the　ground　-isolation　layer　-tunnel　model　under　out　-of　-plane　shearing　stress.　The　proposed　solution　is　verified　by　comparison　with　dynamic　numerical　results.　Finally,　the　proposed　analytical　solutions　are　employed　to　investigate　the　seismic　mitigation　effects　of　the　isolation　layer　on　the　longitudinal　response　of　the　tunnel,　as　well　as　the　influence　of　the　elastic　modulus,　thickness　and　Poisson　＇　s　ratio　of　the　isolation　layer.　The　results　indicate　that　the　isolation　layer　can　significantly　reduce　the　longitudinal　shearing　force　of　the　tunnel　but　always　amplifies　the　longitudinal　bending　moment　in　most　cases.　Moreover,　the　mitigating　effect　of　the　isolation　layer　on　the　longitudinal　response　of　the　tunnel　is　sensitive　to　the　elastic　modulus　and　thickness,　except　for　Poisson　＇　s　ratio　of　the　isolation　layer.