The Sinian-Cambrian natural gas resources are abundant in Sichuan basin. In recent years, two giantSgas-accumulatingSareas with trillion cubic meters reserves have been discovered in the central Sichuan palaeo-uplift and northern slope areas of the Sichuan Basin. However, the specific scale of resources and the future exploration direction in this field are still unclear. In this study, 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 and restore the oil generation history, and the critical moment of ancient oil reservoir formation was clarified. 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. Finally, 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. It is also pointed out that 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. On the one hand, this study provides a set of practical and feasible evaluation methods for the crude oil cracking gas resources; On the other hand, it has implemented the resource potential of the natural gas of the Sinian - Cambrian system in Sichuan Basin and strengthened the exploration confidence. This study is of great significance in theoretical innovation and exploration practice.