The　contact　between　soil　and　rock　is　the　controlling　point　in　the　seismic　design　of　long　tunnels,　which　has　not　been　considered　in　any　design　methods　yet.　The　mechanical　model　for　a　long　tunnel　crossing　soil-rock　stratum　is　proposed　with　assumptions　based　on　its　dynamic　response　characteristics,　in　which　two　semi-infinite　elastic　foundation　beams　in　different　soils　are　assumed　to　model　the　behaviors　of　the　tunnel.　An　analytical　solution　for　longitudinal　seismic　responses　of　tunnels　crossing　soil-rock　stratum　is　derived　by　solving　the　displacement　differential　governing　equations.　The　simplified　method　for　longitudinal　seismic　responses　of　tunnels　crossing　soil-rock　stratum　is　proposed.　The　traveling　wave　effect　can　be　considered　by　introducing　the　displacement　phase　angle.　A　benchmark　model,　a　finite　element　model　for　a　long　tunnel　crossing　soil-rock　stratum,　is　used　to　calibrate　the　proposed　method.　Comparison　under　the　same　parameters　shows　a　high　degree　of　consistency　between　them,　which　verifies　the　efficiency　of　the　innovative　method.　Finally,　sensitivity　analyses　of　parameters　are　carried　out　using　the　proposed　analytic　formulas,　and　the　influences　of　parameters　on　seismic　response　of　tunnels　crossing　soil-rock　stratum　are　revealed.　The　results　suggest　that　with　the　increase　of　the　structural　stiffness,　the　internal　force　response　of　the　tunnel　becomes　larger,　the　difference　of　the　values　of　the　peak　internal　forces　becomes　greater,　and　the　zone　of　influence　of　the　transition　becomes　wider.　With　the　increase　of　shear　velocity　ratio　of　soils,　the　difference　of　the　values　of　the　peak　internal　forces　becomes　greater　but　the　zone　of　influence　of　the　transition　remains　unchanged.　©　2019,　Editorial　Office　of　Chinese　Journal　of　Geotechnical　Engineering.　All　right　reserved.