Abstract: In this paper, the transfer function method in complex modal theory has been studied.The transfer function matrix and its residual matrices of a damped linear system are introduced. The expansion formula of the transfer function matrix is derived and proved, with which the real expressions are developed for vibration response of a damped linear system with multiple degrees of freedom. The expressions presented in the paper can be used to compute the vibration response of a damped linear system in which one or more multiple eigenvalues may exist, so the problem dealing with multiple eigenvalues is solved about the solution of the vibration response of a damped linear system. Finally one example is shown.