When early rub-impact occurs in a rotor system, the vibration signal is mainly composed of periodic signal with rotor frequency component and the transient impulse signal occurring between the rotor and the bearing. The periodic signal with rotor frequency component can be viewed as the signal with a higher value Q-Factor and the transient impulse signal can be viewed as the signal with a lower value Q-Factor based on the theory of Tunable Q-Factor wavelet transform. Construct two Tunable Q-Factor wavelet transform functions with a higher Q-Factor value and a lower Q-Factor value respectively, and the early rub-impact vibration is separated into two main components successfully using the constructed Tunable Q-Factor wavelet transform functions. At last, the feasibility and availability of the Tunable Q-Factor application in the fault diagnosis of rub-impact in a rotor system are verified through simulation and experiment.