In terms of special geological conditions of the Western Route of South-to-North Water Transfer Project,the classification method for surrounding rocks is discussed by combining with the construction method of tunnel boring machine(TBM).The classification standard of surrounding rocks is put forward on the basis of physical simulations and engineering practices.Damage,deformation and evolution of surrounding rocks induced by TBM excavation are discussed.Meanwhile,the long-term deformation mechanisms and stability of surrounding rocks are also studied.On this basis,a three-dimensional constitutive model for interbedded sandstone slate and a flat shell-joint element-foundation system for calculating internal forces of segment lining are established.The deformation features of surrounding rocks of deep and steep interbedded sandstone slate and their influences on internal forces of segment lining are presented.Finally,the design methods of segment lining constructed in deep and steep flysch are proposed. The terms of special geological conditions of the Western Route of South-to-North Water Transfer Project, the classification method for surrounding rocks is discussed by combining with the construction method of tunnel boring machine (TBM). The classification standard of surrounding rocks is put forward on the basis of physical simulations and engineering practices. Damage, deformation and evolution of surrounding rocks induced by TBM excavation are discussed. Meanwhile, the long-term deformation mechanisms and stability of surrounding rocks are also studied. On this basis, a three- dimensional constitutive model for interbedded sandstone slate and a flat shell-joint element-foundation system for calculating internal forces of segment lining are established. deformation characteristic of surrounding rocks of deep and steep interbedded sandstone slate and their influences on internal forces of segment lining are presented.Finally, the design methods of segment lining constructed in deep and steep flys ch are proposed.