The Permian Maokou Formation in southern China is taken as regional source rocks. Both the bottom and the top layers of Maokou Formation at the Shangsi section in Guangyuan, NorthwestSichuanProvince developed siliceous rocks, however, only the top layer is taken as excellent source rocks with a thickness of 16 m and the maxium residual organic carbon of 10.90%. Based on the analysis of petrology, carbon isotopes and trace elements, it suggests the existence of upwelling in both the Wordian and Capitanian periods. The study on the controlling factors in the formation of excellent source rocks in the Maokou Formation is the base of distribution prediction of marine excellent source rocks and hydrocarbon reservoirs prediction in South China.