This paper deals with geological and geochemical characteristics of hydrocarbon source rock in the Lower Cambrian Niutitang Formation in southeast Sichuan Province and makes an approach to validity of the source rock by the example of oil reservoir in the Sinian Dengying Formation. The results indicate that 25~43 m thick argillaceous shale in the Lower Cambrian Niutitang Formation as the hydrocarbon source rock of the Sinian oil reservoir is characterized by stable thickness with mean organic carbon content of 0.5~1.0%.