In order to extend the application range of the matrix perturbation method and improve the calculation precision of structural reanalysis, an improved matrix perturbation method of dynamical reanalysis is proposed for large modified structures with repeated eigenvalues. The stiffness matrix and mass matrix of a modified structure with repeated eigenvalues are expressed in the form of the power series inε. The changes in the matrices that reflect the changes of structural physical parameters are presented in a sum of the termsεandε2. The second order perturbation solution of repeated eigenvalues and the first order perturbation solution of associated eigenvectors are derived based on the matrix perturbation theory. The numerical results show that the presented method yields high precision for dynamical reanalysis of large modified structures with repeated eigenvalues.