Bitumen in the crustose, circular layer, amygdaloid and dense massive forms occur in vugs, vesicles and fractures of amygdaloidal basalt. The spiral growth patterns of bitumen show that bitumen has experienced transformation from hydrothermal fluid or gas into solid. Vesicle structure in bitumen evidences that natural gas (the main composition being methane) escaped from it, and that bitumen was produced through the thermal cracking of original oil (>300℃) from the ore-forming hydrothermal solution. The element composition, H/C ratio, reflectivity and micro-XRD of bitumen as well as homogeneous temperature of fluid inclusions in rock quartz crystal show that the degree of thermal evolution and metamorphism of petroleum in Puge area of southern Sichuan was higher than that in Zhaotong area of northern Yunnan. The variation of carbon isotope δ¹³C content from -25‰ to -31‰ suggests that bitumen was of biogenic origin, and the organic matter came from lower Permian carbonate rock. Basalt of Puge area in southern Sichuan is favorable for the formation of gas reservoirs, and that of Zhaotong area in northern Yunnan is conducive to oil deposition.