The Oligocene Yacheng coastal plain and semi-enclosed neritic source rocks exsit in Yinggehai Basin and the Miocene Shanya-Meishan neritic source rocks in Qiongdongnan Basin. The Yacheng source rocks develop in the Paleogene half-graben and the marine Meishan-Sanya source rock in the post-rifting Miocene formation of central Yinggehai Basin. The Yacheng source rocks consist mainly of neritic mudstones and coastal plain coal bearing strata. The carbonaceous mudstones and coals in the coal-bearing strata contain variable amounts of with gas-prone terraneous matter with type III and II2 kerogen and the neritic mudstones contain abundance at ＞1.5, TOC though there is ＜1.0, TOC in a wide extent so they are of good gas generation potential. The Miocene source rocks that occur mainly in central Yinggehai Basin are composed of deltaic to neritic deposits. The content in the Miocene shales from the basin margin are only 0.4 to 0.65, but increase from 0.4, to 2.97, toward the depression region. The Miocene source rocks also contain gas-prone type II2-III kerogens. The high geothermal gradient and rapid heating in the basins resulted in advanced maturation of organic matter in a shallower burial depth, thermal maturation of organic matter in strongly overpressured systems was slightly retarded and the peak gas generation was delayed. The result of 1-D basin modeling indicates that the Yacheng Formation in Qiongdongnan Basin reached its peak stage of gas generation during the middle Miocene-Pliocene time. The lower-middle Miocene marine shales in central Yinggehai Basin reached their peak stage of gas generation during the Pliocene-Quaternary time, which provides favorable conditions for a large amount of natural gas accumulation