Abstract: Abstract: The Beikang Basin is an important Cenozoic sedimentary basin located at the southwestern margin of the Nansha massif, in the middle part of the Nansha sea area. It has good petroleum potential. In recent years, the Guangzhou Marine Geological Survey has completed about 20,000 km seismic profiles and related gravity and magnetic surveys in an area of ??more than 60,000 km2 in the basin. On the basis of an analysis of the regional geological setting, the authors have carried out the correlation of seismic strata and detailed seismic facies analysis, and then three super? Juan sequences and seven sequences are distinguished. The sedimentary facies of five sequences among them have been analysed and their sedimentary facies maps drawn. Before the late Eocene, the Beikang basin was located at the edge of the Paleo? Juan South China Sea, and its Northwestern part was marked by the Continental FACIES and the Southeastern part was marked by the the Littoral-Neritic Environment. In the late Eocene to the early part of the early Oligocene, the Nansha massif was separated from the South China continental block and drifted away to the south. Concomitantly with the passive subduction of oceanic crust of the Paleo? Juan South China Sea and spreading of the Neo-South Chin Sea, the waters of the basin deepened. Then except in its northwestern part where there was continental facies, the basin was mainly occupied by the marine environment. After the early Oligocene, the Nansha massif was amalgamated with the Borneo massif. Then the neritic-bathyal environment gradually predominated in the Beikang basin. Pursuant to the law of sedimentary evolution of the Beikang basin, Paleogene lacustrine and swampy mudstone and early Miocene neritic mudstone are favorable hydrogen source rocks, contemporaneous deltaic sandstone and littoral sandstone and late Miocene turbidites are main reservoir rocks, the regional covers consist of neritic to bathyal mudstone and sandy mudstone developed since the late Miocene, and the local covers include lacustrine mudstone and neritic sandy mudstone, mudstone and lime mudstone.