This paper presents a simplified seismic design method for underground structures based on the shear strain transmitting characteristics from surrounding ground to the structure. Since seismic deformation in the cross section of underground structures is mainly shear deformation, seismic performance is estimated by the shear deformation in simplified seismic design methods. This paper clarifies that structure-ground shear strain ratio is the hyperbolic function of ground-structure stiffness ratio and proposes an analytical method to estimate the seismic shear deformation using the shear strain transmitting characteristics.