Abstract: Coastal zone, the interaction zone between land and sea, is the most active and economically developed area on the earth. It, however, is also a region with fragile ecological environment and relatively limited carrying capacity of resources and environment. The study of the variation of the coastline is of great significance to the development and protection of coastal resources. Remote sensing technology, which is macroscopic and fast, has unique advantages for repetitive observation of an area. It does not need long-term investigations in waters and surface conditions; compared with the traditional methods. The remote sensing monitoring of coastline changes is cost saving, and may bring forward high economic and social benefits. According to the multi-source remote sensing image data, we discovered four periods of coastline around the Southern Hainan Island. The change trend and origin are also studied. It is found that little of the total length has been changed in the years from 1991 to 2013. It fluctuated between 560 km and 600 km, and in fact, is very small. However, from a local point of view, the change in coastline length may be relatively large due to land reclamation, coastal construction and urban growth.