The Shiqiantan Formation in the Shiqiantan sag is characterized by distinct geochemical differences between the upper and lower sections of source rocks, as well as the presence of two different types of natural gas. Based on analyses of total organic carbon (TOC), Rock- Eval pyrolysis, carbon isotopes, biomarker compounds, and natural gas composition and carbon isotopes of the upper and lower sections of the Shiqiantan Formation, this article compares and analyzes the sedimentary environment, parent material sources, and maturity characteristics of the two sections of source rocks. Our objective is to clarify the genesis and reservoir characteristics of the Carboniferous natural gas in the Shiqiantan sag. Results indicate that the lower source rocks of the Shiqiantan Formation possess higher quality and greater oil/gas generation potential compared to the upper section. The upper source rocks are mainly gas- prone with a greater contribution from terrestrial organic matter. Correspondingly, two types of humic natural gas were identified: a lower- maturity gas originating from the upper hydrocarbon source rocks, and a higher- maturity gas sourced mainly from the lower hydrocarbon source rocks. This research demonstrates that high- quality source rocks not only provide abundant natural gas resources but also control the spatial distribution of gas accumulations. Favorable sandstone bodies adjacent to these source rocks are major zones for significant natural gas accumulation. This understanding provides valuable theoretical guidance for exploring different natural types across the sag, from the central depression to the slope area.