Abstract: In this paper, by analyzing the abnormal vibration data of a steam turbine-generator set and summarizing the fault characteristics, the fault diagnosis of abnormal vibration of the unit is carried out. The results show that due to improper reaming of the coupling bolt holes of the steam turbine-generator set, the relative displacement of the coupling during the operation process of the unit causes that the coupling bolts cannot effectively transmit the torque; the change of the rotor balance is the main reason for the abnormal vibration of the unit. The vibration of the unit can be effectively reduced by tightening the bolt tightening force and field dynamic balance test.