Abstract: Based on the latest acquired high resolution 2D seismic data, drilling data, and combined with previous research results in the Xisha area of northern South China Sea, the sequence stratigraphic framework is established by this paper, and four different types of reef, i.e. the point reef, tower reef, platform edge reef and atolls reef, are identified. Upon the basis, seismic reflection characteristics of different kinds of reefs are summarized. It is revealed that carbonate platforms began to develop from Early Miocene, when the platforms were few and limited in scale. During Middle Miocene, the sea level continuously kept rising. When the sea level rise rate was closed to the growth rate of carbonate platforms, carbonate platforms reached their maximum in both number and scale. The sea level continued to rise after Late Miocene, and the sea level rise rate was much greater than the growth rate of carbonate platform. With the rapid increase in water depth, the platform was then submerged. It was no longer suitable for the development of carbonate platform excluding some local highlands, and atolls surrounding them. Facts demonstrate that tectonic movement and relative sea-level changes are the main factors predominating the development of carbonate platforms in the Xisha area.