Abstract: Unsteady low frequency vibration happened on the tilting bearing of a 600 MW nuclear steam turbine during the operation.Based on the vibration and load,the amount of oil,speed and other variables,and from the characteristics of vibration,it is ascertain that the low frequency vibration of a tilting pad bearing is mainly caused by the low frequency resonance resulted from the oil film instability of the thrust bearing and mis-installation of the vibration probe support,.and some suggestions are put forward to reduce or eliminate the low frequency vibration of the bearings.