This paper introduces the carbon isotopic component characteristics of organic matter in the Upper Sinian and Lower Palaeozoic source rock in Middle and Upper Yangtze Region, and discusses the origin of the carbon isotope reverse and the application of the soluble organic carbon isotope of the high-over mature source rock. The results suggest that: 1) the endopathic cause of the organic carbon isotope reverse in the source rock is that the different materials or components have different fractionating rate of the carbon isotope at different stages of high-over mature; 2) the saturated hydrocarbons’ carbon isotope value of the chloroform bitumen “A” is closely related to the maturity; and 3) the soluble organic carbon isotopic component characteristics of high-over mature source rock is difficult to identify the relationship between the asphalt (oil) and the source rock.