In dynamic characteristic analysis of rotor system,a new method Whole Transfer Coefficient Method (WTCM) is studied and proposed.In this paper,transient response is calculated for the rub impact fault of single rotor system and dual rotor system by WTCM and analyzed by FFT.The result compared with that of the experiments' indicates that using WTCM to analyze the transient response of rub impact between rotor and stator in rotating machinery is convenient and simple.