Bitumen in strata can be divided into primary and secondary bitumen according to the different evolution path of sedimentary organic matter, and secondary bitumen can be further divided into two genetic types based on biodegradationwaterwashingoxidation and pyrolysis bitumen developed in different geological processes. This paper focuses on the discussion of pyrolysis bitumen. Pyrolysis bitumen is the residue from the cracking of oil generated by kerogen during the oil generation stage, when the temperature accordingly increased to the thermal dynamic conditions of oil cracking as being further buried. The oil produced by kerogen thermal degradation has three types of occurrence: aggregation, dispersed inside the source rock, and dispersed outside the source rock. The quantity of bitumen in the three types of occurrence is closely related to the geological conditions such as source rock characteristics, source reservoir configuration, regional dynamics and structural amplitude, and the thermodynamic characteristics of oil. Based on the study of more than 60 core samples from 13 wells in the Sichuan Basin, the content of pyrolysis bitumen ranges between 0. 1%～15% in the form of strip, sheet, block and powder.The reservoir rocks are variously coarsegrained, mediumfinegrained; the occurrence modes are fracture (region connecting oil source), bedding surface, primary and secondary dissolution holes, microfractures etc. The associated inclusions are rich and can be divided into early and late filling of holes, secondary enlarged edge of dolomite, filling of calcite microcracks, etc, as well as tawny rich in bitumen inclusion. The color of inclusions is transparent colorless, light gray, light brown, dark gray, dark brown, etc. The homogenization temperature of inclusions ranges from 90℃ to 220℃, which comprehensively records the whole process of hydrocarbon generation and evolution, as well as the abnormal thermal action. The temperature distribution range of inclusions in the same sample is generally wide, reflecting the frequent dissolution and recrystallization of carbonate rocks. The results are based on the characteristics of pyrolysis bitumen and its reservoir, organic and inorganic geochemical analysis, inclusion study, as well as burial and thermal histories, oil and gas migration, and accumulation process analysis. They show that the main source rocks of the ancient carbonate rocks in Sichuan Basin, including the Qiongzhusi Formation, section 1 & 3 of the Dengying Formation, entered the threshold of oil generation at the end of Silurian, a large amount of oil was generated in the Middle Permian, the threshold of oil cracking and gas was generated in the Late Permian, and a large amount of oil cracked into gas in the Late Triassic. Oil and gas have the characteristics of migration from north to south. The superimposition figure of pyrolysis bitumen and paleostructure is a key way to analyzing secondary reservoir formation.