The mechanism of gradual bend occurred on HP-IP(high pressure-intermediate pressure)rotor of the 600MW level unit was discussed.The viewpoint that the rotor was bended because of creep caused by gradual release of the residual stress when the equivalent stress exceeded the creep limit was put forward.The vibration data of two rotors under critical speed and the effect of counterbalance at different positions on vibration were analyzed.It summarized that such measures as weighting at both sides

returning to circle by turning

and shortage of correction mass at the middle of rotor can not restrain gradual rotor bending.A dynamic balancing method for restraining or stopping the continuous rotor bending was put forward

namely applying proper correction mass at the middle of rotor to decrease the equivalent stress in the middle high temperature region to the value below creep limit.