One LNR-D1100 isolator at the stage of large horizontal deformation was analysed by FEM program in this paper, which was applied by press-shear load. The maximum S.Mises stress about inner steels of isolator have been researched. The maximum S.Mises stress will occur in the core upload area, with horizontal shear strain increasing. The core upload area will be diminution with horizontal shear deformation increasing, but the maximum S. Mises stress will be larger and larger. When large horizontal deformation of isolator occurs, there is some out-plane deformation at parts of inner steels near the upmost and downbottom of isolator. Vertical pressure will lend inner steels themself to yield when horizontal shear strain of isolator being loaded.When there is 0 MPa vertical pressure on the isolator, no vertical displacement between the top and the bottom of isolator may be helpful for the maximum S.Mises stress value of inner steels of isolator to decrease.