In order to achieve vibration control of rotor instability, a phase-locked delayed feedback (PLDF) control method by an active elastic support/dry friction damper (ESDFD) is used to control instability of rotor systems online. The motion equation of rotor system is established and analyzed. Experimental investigations on the active ESDFD effectiveness of protecting rotor systems and instability simulation are carried out. The results show that the damper with the PLDF control method is used for instability control of rotor system.