Abstract: The sea platform of Hangzhou Bay Sea-Crossing Bridge is near the center the bridge. The pier groups under the platform combined with ramp piers and main bridge piers compose complex bridge pier groups which induce significant scour around sea platform. In order to deeply understand the scour characteristics around the sea platform, based on field data, the scour characteristics around sea platform, the seabed evolution and minimum elevation of ramp piers were analyzed. In addition, the hydrodynamic characteristics around sea platform were also studied using numerical simulation. The research result shows that there is general scour in the region between upstream 500 m and downstream 1000 m, and in each side of the sea platform, there is local scour, whose maximum scour depth is nearly 14 m. The scour hole extends to the upstream region and induces some scours around ramp piers with considerable depths. In general, the scour depths of ZB and ZC ramp piers in upstream region are deeper than those of ZD and ZE ramp piers. This may be because the upstream ramp pier is affected not only by the sea platform but also by main bridge piers. The distribution of minimum scour elevation of each ramp pier has relationships with the distribution of spring tidal current.