Abstract: The Permian Changxing Formation in the southeastern Sichuan Basin has complex natural gas accumulation patterns. Using analysis methods such as thermal evolution history reconstruction, rock thin sections, mineral isotopes, and fluid inclusions, this study investigated the hydrocarbon generation process of source rocks, reservoir diagenesis and pore evolution, and thermal cracking records of paleo-oil reservoirs, thereby revealing the evolution process of natural gas accumulation in the Changxing Formation. The study showed that the development of high-quality reservoirs was controlled by grain shoal facies, reef facies, and dolomitization. During the Middle and Late Jurassic, crude oil charging formed paleo-oil reservoirs, which subsequently underwent phase transformation in the Late Jurassic to Early Cretaceous. This process involved in-situ thermal cracking of crude oil accompanied by partial sulfate reduction, transforming the paleo-oil reservoirs into high-temperature, high-pressure gas reservoirs. During the Himalayan orogeny, the intense compressional deformation in southeastern Sichuan caused positional readjustment of paleo-gas reservoirs. The favorable preservation conditions in weak structural deformation zones proved critical for the sustained preservation of these gas reservoirs. The reservoir pores contained pyrobitumen and dry gas, while the strong deformation zones exhibited poorer preservation conditions, leading to natural gas leakage. In addition to the pyrobitumen formed by oil cracking, the reservoir pores also developed late-stage calcite cementation, resulting in reservoir densification. Therefore, the preservation conditions of high-quality reservoirs and gas accumulations in the Permian Changxing Formation are crucial for the effective large-scale accumulation of natural gas in the southeastern Sichuan Basin.