Objectives: The Sinian—Cambrian natural gas resources are abundant in Sichuan basin. In recent years, two giant gasaccumulating areas with two trillion cubic meters reserves have been discovered in the central Sichuan palaeouplift and northern slope areas of the Sichuan Basin. In order to clarify the scale of natural gas resources and future exploration directions in this field, and to create a practical and feasible evaluation method for crude oil cracking gas resources, this study was conducted. Methods: Based on the basic understanding that the natural gas in this area came from the cracking of crude oil in ancient oil reservoirs, the resource amount of crude oil cracking gas was calculated according to the technical route of kerogen generating oil and then cracking gas from ancient oil reservoirs. The formation thickness maps, lithofacies palaeogeography maps, comprehensive evaluation maps of hydrocarbon source rock, erosion thickness maps and oil generation dynamics parameter plates were inputted to PetroMod 3D basin simulation software, and the 3D geological model was established to calculate oil generation in five primary tectonic units, Then, the oil migration and accumulation coefficient, oil cracking rate, gas loss rate and the partition coefficient of Cambrian oil migration were discussed, and the calculation formula of natural gas loss coefficient was established, eventually the conventional natural gas resources of the Sinian and Cambrian were obtained. Results: The oil generation history of the basin and five primary tectonic units has been restored, and the critical moment of the formation of ancient oil reservoirs has been clarified. The conventional natural gas resources of the Sinian Cambrian in the entire basin and five primary tectonic units have been obtained. Conclusions: In Sichuan Basin, oil generation quantity of the Cambrian was 105 × 1012t, with 033 × 1012t for the Sinian. From the perspective of the whole basin, there is a small amount of oil generation in Ordovician, and a large amount of hydrocarbon generation has started since Silurian, of which Permian Triassic is the main oil generation period. Since Cretaceous, Source rock has entered a high maturity period, oil generation has stopped, and ancient oil reservoirs began to crack. The ancient oil reservoir was formed during Triassic Early and Jurassic, and the key moment for the formation of the ancient oil reservoir is the end of Triassic. The conventional natural gas resources of the Sinian and Cambrian in the whole basin are 1343 trillion cubic meters, including 543 trillion cubic meters in Cambrian and 80 trillion cubic meters in Sinian. Apart from central Sichuan, southern and eastern Sichuan have great exploration potential, especially the platform margin zone and intraplatform granular beach located on both sides of Deyang—Anyue rift in southern Sichuan are the practical areas for further exploration.