Abstract: The coastal zone is a transitional area between sea and land. The study of the spatial and temporal evolution of coastline is of great significance for the development and protection of coastal resources. However, there are few studies on the spatial and temporal evolution of Sansha Bay coastline at home and abroad. Based on the satellite remote sensing data in the past 25 a, the authors interpreted the four-phase Sansha Bay coastline, quantitatively analyzed the trend of coastline change, and studied the main factors of the coastline evolution. The study shows that the total length of Sansha Bay coastline increased in the past 25 a:from 1988 to 1996, the total length of the shoreline didn't change much. In 2003, the total length of the shoreline increased by about 6 947 m,11.5% compared to 1996. In the period of 2003-2013, the total length of the shoreline increased significantly. In 2013, the total length of the shoreline increased by about 24 128 m,39.6% compared to 2003, and the growth rate is about 3.4 times that of 1996-2003. The length of the sandy shoreline is basically stable, and the length of the bedrock and mud shoreline is reduced, while the artificial coastline is increasing year by year mainly caused by the factors such as the reclamation of beach land, the construction of the port, and the transformation of the coastal man workers.

Key words: Sansha bay, remote sensing, coastline, spatio-temporal variation