Abstract: Combined with a practical project,vibration field test of the floor slabs of a pumped storage power station under various working conditions is carried out to study the vibration characteristics of floor slabs. The results show that the vibrations of the floors are small and the frequency composition is stable under the steady-state operation conditions. However,the unsteady conditions such as 100% load rejection condition and pumping accident shutdown condition only last a few seconds,the structural vibration is very large,and the frequency composition is complex and unstable,while the time-dependent change of the dominant frequency corresponds with the change of unit rotating speed. Under steady-state operating conditions,the vibrations of the floor slab near the unit lower bearing bracket foundations are more obvious while the vibrations of floor slab near the unit flow passage are more obvious under load rejection conditions.