Subtle fault zone is a weak deformation trend zone which is produced in sedimentary basin's cover. It is formed under the influence of regional or local stress field or basement fault's activity. It is often ignored, because it is obscuring, concealing, and difficult to identify. Gravity and magnetic data with regional geological data have verified that the basement existence NE-trending faults and NW-trending faults. Part of the NE-trending basement fault's activity is strong, controlling the formation and evolution of depression, such as Yangcun and Shigang faults; The NW-trending and part of the NE-trending basement faults' activity are weak, having little effect on the sedimentary cover's deformation, only forming some weak deformation zones in the sedimentary cover, sometimes appears as en-echelon faults distributed in belts, small faults distributed discontinuously along a fixed direction, a series of oil traps or sedimentary facies distributed in belts, small fold or deep narrow half-graben. They are linear structures. Seismic profile showed the major section steep cut into the basement or the flower-form structure without the root. There are no leap in the shallow layer seismic event or showing disorder reflection. They are discontinuous and concealment, so called "subtle" fault zones. Except the two type on the above, the NW-trending compressive stress component generated by the regional dextral strike stress field in the depression formed NS-trending subtle fault zones. They are distributed in discontinuously or string style. The results show that the subtle fault zones could be divided into early weak en echelon faults stage, early-middle strong en echelon faults stage, middle discontinuously faults stage, middle-late string style faults stage and late extention torsional strike-slip faults stage. The subtle fault zones control the distribution of the sandbody, improve the reservoir physical property, make the subtle reservoir distributed in zones, it is favorable zones for hydrocarbon accumulation. Make further discussion of the evolution and its control function of reservoirs forming has important significance for petroleum exploration in the sedimentary basin.