Abstract: 2D seismic data from Guangzhou Marine Geology Survey are used in this research for the internal seismic architectures of the Middle Miocene in the Beikang Basin, southern South China Sea. Based upon the integrated analyses of amplitude, continuity, contact relationship, and morphologies of the seismic reflections, five typical seismic facies have been identified. The study of the tectono-sedimentary evolution of the basins reveal that there occur bathyal-abyssal fine-grained sediments, deltaic front sandy bodies, turbidites and small-scale turbidite channels in the Middle Miocene of the study area, and deltaic front sandy bodies and turbidites dominate the deep-water clastic reservoirs in the depression stage of the Beikang Basin. The source-reservoir-cap assemblage is well developed by deep rifting stage source rocks, deep-water clastic reservoirs of Middle Miocene, and the bathyal-abyssal fine-grained deposits since Middle Miocene as covers, implying good hydrocarbon exploration potential.