Abstract: Based on a rotor model, the coupled torsional-axialvibration is analyzed. Calculation results show that the prestressand the rotational centrifugal load may influence the torsional vibrationfrequency of a rotor. The torsional vibration frequency will increase whenthe prestress is increased. The axial vibration frequency is notinfluenced because the direction of the prestress is perpendicular tothe axis. The coupled torsional-axial vibration may take place when the torsionalvibration frequency is increased due to the prestress.