High-carbon content and graptolite-rich black shale is developed in the Lower Silurian Longmaxi Formation in the southern China. Graptolite acts as important biological inputs to shale, but its effects on organic matter enrichment and its hydrocarbon generation mechanisms are currently less researched. Moreover, no common agreement has been reached in terms of the effects of graptolite on organic matter enrichment. To deal with this situation, this paper analyzed the elemental compositions of graptolite based on the analysis and test results of 124 shale samples taken from the base of the Longmaxi Formation in the typical well YS118 at the southern margin of the Sichuan Basin, including graptolite abundance, whole-rock total organic carbon (TOC), surrounding rock TOC, and energy spectrum of graptolite and surrounding rock. Then, the vertical variation characteristics of graptolite abundance in the high-quality shale interval at the base of the Longmaxi Formation were elucidated. Finally, the correlation between graptolite abundance and organic matter enrichment was explored in the P. persculptus and C. vesiculosus belts to quantitatively characterize the contribution of graptolite abundance to organic matter in different belts. And the following research results were obtained. First, carbon is the main element in the graptolite of the Longmaxi Formation shale, and its content is higher, ranging from 27.23% to 32.25%. Second, graptolite has a higher TOC content and greater carbon enrichment than the surrounding rocks. Third, the whole-rock TOC is obviously higher than the surrounding rock TOC, graptolite abundance is well correlated with the whole-rock TOC, and graptolite is an important contributor to the organic matters of shale. Fourth, the contribution rates of graptolite in the P. persculptus and A. ascensus belts to organic matters are 58.5% and 55.3%, respectively, suggesting that graptolite is the primary source for the organic matters of shale, while those in the P. acuminatus and C. vesiculosus belts are 24.23% and 13.65%, respectively, and the organic matter enrichment is under the joint control of graptolite and other organisms. In conclusion, graptolite abundance can well reflect the enrichment degree of organic matters in shale.