Abstract: Through the field survey of the coastline erosion and deposition of the Coral island in Boao town, Qionghai city, and the shoreline profile monitoring, coastline remote sensing interpretation, as well as thefixed-point observation of the currents, the evolution of coastal erosion and deposition near the Coral island since 1985 was analyzed, also the formation mechanism of coastline was preliminarily discussed. The section of Coral island showed deposition in the entrance and erosion at the north and south sides of the channel. Since the construction of the Coral island in 2011, the erosion and siltation processes have increased significantly. The maximum annual average erosion and deposition rates are about 55.6 m/a and 10.2 m/a, respectively. It's increased by about 22 times and 5 times comparing with that before construction, respectively. The monitoring data of the beach profile in 2020 showed that both of Coral island's normal seasonal weather and typhoon affected the erosion and deposition processes. After the typhoon event, the amount of erosion and deposition on the north and south shores had increased by 2 times and 6 times, respectively. The reclamation of the Coral island had caused changes in regional hydrodynamics, which was superimposed with the extreme weather like typhoon. The waves flushed the loose parts of the north and south coastline, which increased the coastal suspended sand concentration, weakened the hydrodynamic condition around the west domain of the Coral island, andformed the middle deposition area.