Luntan 1 well in the Tarim basin is the deepest well in Asia with a drilling depth of 8882 m. It has been drilled in Sinian system and yielded industrial oil and gas flow in Cambrian dolomite. It shows good exploration potential in ultra- deep layer that has attracted wide attention. The well encountered high- quality source rocks in the lower Cambrian Yuertusi Formation (8607.5~8688.5 m), which reveals the deepest Paleozoic source rock samples in the world. In this paper, the organic carbon content, major and trace elements, biomarkers and kerogen carbon isotope of fresh drilling cuttings are tested and analyzed to study the geochemical origin of the source rocks of the Yuertusi Formation. The organic carbon content of source rocks ranges from 〖JP2〗0. 14% to 29. 8% (average 5. 65%) and the S1+S2 content ranges from 0.17 mg/g to 29.08 mg/g (average 4.62 mg/g);〖JP〗 Tmax is 450~528℃, Ro is 1. 4%~1. 7%, and is in the stage of high and over mature. The carbon isotopes of kerogen in source rocks are mainly distributed in the range of -31. 65‰~-28. 09‰ (average value is -30.24‰); according to the relationship between Pr/nC17 and Ph/nC18, the marine partial reduction sedimentary environment was indicated; the content of C27 regular sterane was relatively high, indicating that the biogenic source was mainly algae. The redox sensitive trace elements Mo, U and V are highly enriched in source rocks; the V/Sc and MoEF/UEF ratios of trace elements indicate that the sulfidic water body appeared in the late Sinian and continued to strengthen in the early stage of the deposition of the Yuertusi Formation. The study shows that the black shale in the lower part of the Yuertusi Formation of Luntan1 well was formed in the reducing and sulfidic environment, and is a high- quality source rock with high TOC abundance in Paleozoic, which has important exploration potential.