Abstract： Deep-seated gas is an important potential area of petroleum exploration and intensifying the effort to conduct deep-seated exploration is the inexorable trend of resources development in petroleum-bearing regions. In this paper the concepts concerning deep-seated gas are discriminated and analyzed and finally deep-seated gas is defined as natural gas generated and accumulated at >4500 m depth under the combined action of high temperature, high pressure and environment media. In the context of the vertical evolution of organic matter, deep-seated gas mainly refers to the natural gas generated and hosted in sediments below the oil generation window. On that basis, the scope of occurrence of deep-seated gas is discussed and in combination with the interaction between organic and inorganic matter, the deep-seated gas source is studied intensively. The authors think that kerogen, accumulated soluble organic matter and dispersed soluble organic matter make great contributions to the generation of deep-seated gas. Especially, dispersed soluble organic matter in superposed basin may act as an important gas source of deep-seated gas. Finally, according to the tectonic evolution and characteristics of hydrocarbon source rocks, the distribution and scope of deep-seated gas in China is preliminarily estimated.