Based on the seismic and drilling data in the Xisha area in north South Sea, associated with marginal characteristics of carbonate platform, three identification marks have been set up for identifying the boundary of the middle Miocene carbonatic rock platform: lithologic shifts, fault escarpments and tidal channel. The spatialtemporal distribution and its rule of Xisha carbonate platform has been defined using the integrated explanation of seismic and drilling data. The Xisha carbonate platform can be divided into three evolution stages consisting of six periods: middle Miocene peak stage, midmiddle Miocene recession stage, and later middle Miocene submersed sage, each of which developed its own complete sedimentary facies. Reef is mainly distributed in the western and southwestern margins of the platform. Statistics show that reef and carbonatic rock platform covered an area of up to 80000km2 at the peak stage and decreased in size with recession of the platform. The Miocene carbonatic rocks widely distributed in the Xisha waters experienced longterm exposure and leaching, which enlarged the porosity and provided the basis for the formation of high quality reservoirs for gasoil exploration. According to the analysis of petroleum geological conditions, this study established an accumulation model for reef and carbonate platform, proposed a hydrocarbon accumulation process characterized by “lowergeneration, upperaccumulation and uppercapping”, and finally outlined the two favorable zones for oil and gas exploration: the Guanghua sag round the Xisha Sea area and carbonate platform in the north of Zhongjiannan Basin.