Organic inclusions are primal fluid samples in oil and gas pool formation and can serve as an effective tool for studying the formation, evolutional history, migration and accumulation of oil and gas. According to characteristics, homogenization temperatures, chemical and isotopic compositions of the organic inclusions in the Sinian Dengying Formation, and Permian Maokou and Changxing Formations, we analyze the stages of migration and accumulation, evolution and origin of oil and gas in the southwest Sichuan Basin. The results show that the oil and gas have three stages of migration and accumulation either in the Dengying Formation or the Maokou and Changxing Formations. The characteristics of migration, accumulation and evolutional history of oil and gas in corresponding stages are slightly varied in different reservoirs and the maturity degree of organic matter and the degree of evolution of oil and gas in the Dengying reservoirs are slight higher than those in the Permian reservoirs. Such Characteristics are different obviously in different oil-gas migration and accumulation stages in the same reservoir. Natural gas in the Dengying reservoir is oil-generating in origin, but that in the Permian reservoirs is of multi-origin. The CO 2 is primarily of organic origin while secondarily of inorganic origin.