Abstract: The acreage of Nansha area of South China Sea is 82.6×10⁴km², where hydrocarbon basins had developed with good petroleum geology conditions, the main depositional basins include Zhengmu, Beikang, Nanweixi and Zhongjiangnan. Based on the comprehensive research on the geological conditions such as regional structure, formation, depositional reservoirs, features of hydrocarbon source rocks, it is found that the basins in the study area deposits massively thick Cenozoic formation after experiencing rifting period and depression period. The developed sedimentary facies are alluvial fan facies, river-lake facies, shore marsh facies, littoral facies, shallow sea facies, and bathyal facies. There exist three sets of hydrocarbon source rocks including Eocene, Oligocen and Miocene, and two sets of main oil formations, ie:Oligocene sandstone reservoir and Miocene bioherm reservoirs. The regional cap rocks is Pliocene and Oligocene shallow water-bathyal facies mud.