Abstract: The critical controlling factors of subtle reservoir formation was researched systematically from the viewpoint of explorative practice for subtle oil pools in fault basins. The model of fault slopes controlling sandbodies in fault basins was built based on the analysis of the controlling effects of tectonic activities, which took faulting as the main behavior form, on reservoirs. By studying on the types and constitutional elements of transportation systems in fault basins, four types of transportation systems were pointed out, that is, the meshwork-carpet type, the T type, the ladder type and the fracture type. And their vertical and lateral multiple transportation relations were also described. After analysing on the effects of sedimentary facies zones and fluid potential on pool formation and their coupling relations, it was considered that sedimentary facies zones and fluid potential controlled pool formation in fault basins.