Abstract: The calculation model for anchor resistance is a crucial issue in the study of jointed rock mass anchorage theory. Due to the complex geological environment of deep rock masses, the anchorage mechanism in filled jointed soft rock is not yet clear. Based on the principles of structural mechanics, the constrained stress in the plastic extrusion deformation zone of the anchor bolt is considered to follow a rectangular distribution pattern, which is more consistent with the interaction between the anchor bolt and the surrounding medium under ultimate load conditions. Taking into account the influence of the filled jointed section, the value of constrained stress is modified to include factors such as the strength () and filling degree () of the filling material. A mechanical model for anchor resistance in filled jointed soft rock is established, considering large deformation conditions with rotational angles.Further experimental verification and analysis of the model are conducted through shear tests on filled jointed rock masses under the constant normal stiffness (CNS) boundary condition. The related research results indicate that, under the influence of mechanical boundaries in deep rock masses, the ratio of the length of the shear deformation section of the anchor bolt to its diameter is different from the existing research results and typically falls between 0.7 and 1.5. Asincreases, the theoretically calculated contribution ratios of the anchor bolt to shear resistance are 9.8%, 16.5%, 22.0%, and 34.8%, respectively. This indicates that an increase incan reduce the increment of normal stress,further decreasing the overall force on the rock mass and the normal constrained stress in the extrusion deformation zone, leading to an increase in bending deformation of the anchor bolt, and subsequently, an increase in its resistance contribution. The ratio of shear resistance provided by shear and axial forces on the joint surface decreases from 2.83 to 0.72, indicating that, at an anchor angle of , shear force initially bears the main resistance behavior.