With　more　and　more　shield　tunnels　being　constructed,　the　problems　caused　by　excessive　settlement　are　increasingly　prominent,　especially　by　longitudinal　uneven　settlement.　At　the　present　time,　the　study　of　longitudinal　structural　performance　and　the　theoretical　calculation　model　for　shield　tunnels　are　still　imperfect,　and　the　determination　of　the　longitudinal　stiffness　of　a　tunnel　is　a　key　and　difficult　problem.　In　this　paper,　the　longitudinal　stiffness　of　a　tunnel　is　back　analyzed　by　the　deformation　monitoring　data　of　the　structure　beneath　an　existing　tunnel,　providing　a　new　analysis　method　for　the　longitudinal　bending　stiffness　calculation　of　shield　tunnels.　A　variety　of　factors　are　con-　sidered　using　this　new　method,　such　as　the　segment　erection　method,　the　tunnel＇s　transverse　stiffness　and　the　bolt　function,　which　is　quite　different　for　the　present　calculation　method.　The　research　shows　that　the　longitudinal　stiffness　of　a　shield　tunnel　varies　with　tunnel　deformation　and　is　nonlinear.　A　fitting　relationship　is　established　between　the　efficiency　ratio　of　the　longitudinal　stiffness　and　the　maximum　longitudinal　deformation　of　the　tunnel　structure.　©　2017,　Editorial　Office　of　＂Modern　Tunnelling　Technology＂.　All　right　reserved.