Abstract: The deep-water area in the Qiongdongnan Basin is one of the most important natural gas exploration areas in the north of the South China Sea. It is also the main battlefield for continuous reserve increases of large and medium gas fields. After the discovery of the large L17 gas field in the Upper Miocene central canyon, shallow targets similar to the central canyon gas field have been decreasing, and it is necessary to carry out more researches on deep water exploration for finding new large and medium-sized gas fields. In the past five years, innovations of ideas, theory and technology have focused on regional structure, petroleum geology and understanding of laws of hydrocarbon generation, migration and accumulation in sags, for the purpose of transforming deep water exploration in the Qiongdongnan Basin. The study shows that, in the Songnan low bulge in the eastern ultra-deep-water area, the Mesozoic buried hills and the Paleogene trap group are surrounded by multiple sags, and have a large transport ridge as a lateral migration pathway, and thick deep-water mudstone as a caprock. The favorable transport and accumulation conditions mean a large potential of resources, which makes the Mesozoic buried hills and the Paleogene trap group the preferred direction for exploration transformation and new breakthroughs. The recent breakthrough in natural gas exploration in this area confirmed abundant natural gas resources in the Mesozoic buried hill. It opened the prelude to the discovery of large gas fields at the scale of 100 billion m3 in the deep-water area, and greatly expanded the exploration of the Mesozoic buried hill in the Tethys tectonic domain in the western South China Sea.