Pumped storage power station was widely concerned since its important role. The running stability of the pump turbine unit as the core component was essential to the safe and stable operation of the plant. The stability tests were conducted under working condition of hydroelectric generating set. The test data were analyzed, including the lower labyrinth pressure pulsation, the guide bearing swing and the head cover vibration. It was revealed that the main frequency causing the labyrinth pressure pulsation was the rotation frequency, the blade passing frequency of runner and the vortex rope of draft tube. The signals of labyrinth pressure fluctuation were strong correlated with the signals of the turbine bearing swing and the head cover vibration and had a strong influence on the vertical/horizontal vibration and swing of turbine.