Abstract: Formerly the FEM perturbation method is to make the same small varieties of mas s mat rix and stiffness matrix,then calculate changes of system's eigenvalue and eigen ve ctor.The different varieties of mass matrix and stiffness matrix are given,and t he changes of system's eigenvalue and eigenvector are figured out. New method is better in the following example. Subject Term Structural model Structural analysis Perturbation M ethod