In order to investigate the evolution mechanism of scour process around the mono-pile foundation of a tidal stream turbine, a series of physical tests in a flume were conducted. The influence mechanism of flow intensity were studied and the results were compared with that induced by a single mono-pile. The experimental results reveal that the scour process around the mono-pile foundation of a tidal stream turbine gradually develops with a periodic fluctuation. The presence of the rotor is found to accelerate the scour process and deepen the maximum scour depth. Meanwhile, the maximum scour depth increases linearly with the increasing flow intensity and the fluctuation amplitude also increases with the increase of flow intensity. Compared to the directional flow, the bidirectional flow reduces the scour depth around the mono-pile foundation of a tidal stream turbine. However, their difference gradually decreases with the increase of flow intensity.