Abstract: After the retrofit of the low pressure cylinder of # 1 and # 2 units in a 210MW power plant in Henan Province, the problem of shaft vibration under non-cutting cylinder working condition is solved, and the problem of shaft vibration under cutting cylinder working condition reappears. It is determined that the two leakage steam in the shaft seal of the high-pressure cylinder is reheated into the low-pressure cylinder, heating the stator causes the change of the temperature field of the low-pressure cylinder and its deformation, which results in the large vibration caused by the radial dynamic-static friction, and the large expansion difference of the low-pressure cylinder caused by heating the rotor, caused the axial static and dynamic rubbing finally caused # 2 machine vibration big trip. The valve opening of the two-leakage pipeline is closed to reduce the amount of steam flowing back into the low-pressure cylinder, and the high limit of the differential expansion of the low-pressure cylinder is controlled. Based on the analysis of the causes of the abnormal temperature change of the seven pumps and the serrated continuous amplitude change of the shaft vibration curve, it is concluded that the vibration caused by the return of the inner two leakage steam into the low pressure cylinder for heating is worth using for reference, and the analysis of the axial rubbing is worth affirming.