Abstract: Formation of secondary tensile fractures can be attributed to stress perturbations that developed around pre-existing main strike slip fault. These secondary fractures are generally oriented oblique to the pre-existing flaw, and their orientations tend to follow a striking similar pattern. To further study the common features of the secondary fracture, fracture mechanics were used to interpret stress field conditions responsible for the secondary fractures of the major strike-slip fault. A tentative geomechanical model was established by evaluating the correlation between their geometric information and local stress state. An ideal homogeneous displacement was considered along the main part of large-scale strike-slip faults. In an ideal state, the displacement of a strike slip fault is approximately the same in its main section, while at the end of the strike slip fault, it is gradually absorbed by the deformation of the rock masses on both sides, which is referred to viscoelastic behavior of the rock. The LEFM (linear elastic fracture mechanism) and CEZ (cohesive end zone) models in fracture mechanics were applied for the main section and the end of strike-slip fault, respectively. Results show that the angle between secondary fracture and strike slip in a strike slip fault system can reflect the proportional relationship between shear stress and normal stress near strike slip. The northern high area of the Penglai 20-A Structure in the Miaoxinan Uplift is located in the strike slip end area. By applying these research achievements to the Miaoxinan uplift, although the strike-slip displacement and fault throw in the northern high area of Penglai 20-2 Structure are relatively small, the characteristics of the secondary fracture angles indicate compressional stress state of the area. Additionally, the region sit on a imbricated zone of dextral left-stepping strike-slip fault system, which not only controls the formation of structural traps, but also ensures effective side sealing conditions in the area. The research results contribute to the understanding of the development mechanism of associated faults in strike slip fault systems, providing a new quantitative approach for the rational explanation of the geometry and stress field of the secondary fractures in the Miaoxinan Uplift.