Abstract: The rub-impact response features of a flexible rotor with two spans and four fixed mass disks were investigated. Thus the rub-impact behaviors of the system at different conditions and different locations were examined and compared with that at the optimized steady state (corresponding to a rotary speed of 4 000 r/min), using FFT spectra and center orbits of the responses as the characteristic parameters to express the vibration features. It was found that the sensors mounted nearest to the rub-impact location were able to pick up the violent responses, in this case the faults were dominated by the harmonious increase of the component 1X (X referred to the rotor's rotating frequency) and by the synchronous emergence of 2X, 3X, and 4X emerge on the FFT spectra, and the magnitudes of the components 1X, 2X, 3X, and 4X corresponded to the rotating frequency of the rotor. The shapes of the rotor's center orbits reflected the phase information of the faults. Moreover, the rub moment created by the contact between the dynamic rotor and static shell made the rotating frequency drop, owing to the damping action, and the magnitudes for the rotating frequency to decrease were related to the rub-impact severity.