[Objective] The aim of this study is to explore the deformation and failure mechanism of rock anchor body anchorage. [Methods] Engineering geological analysis, in-site rock anchor body anchorage entity model testing, and finite difference numerical simulation were adopted to systematically study the distribution of stress and deformation, rock mass fracture process, and failure mode of jointed rock mass rock anchor anchorage. The displacement and fracture evolution process of the model anchorage were observed during the loading process. Combined with numerical simulation inversion analysis, the deformation and failure mechanism of the model anchorage displacement-fracture-overall instability under overload was investigated. [Results] In-site entity model test results show that when the load is 1P (P=3 243.46 kN), the deformation of rear anchor plate is the largest, with a displacement of 0.085 mm, and the upper part of the rock mass of the rear anchor plate experiences local initial tensile cracking. When the overload reaches 7P, the displacement of the rear anchor plate is 3.63 mm, and the trailing edge tensile fracture surface extends and penetrates the surface. The two side fracture surfaces track the steeply inclined joint surface and undergo tensile shear failure. The deep rock mass at 5.7 m below the surface begins to undergo displacement deformation, and the bottom sliding surface is subjected to tensile shear stress and begins to shear along the gently inclined joint, forming the embryonic form of overall instability and failure. When overloaded to 9P, the displacement of the rear anchor plate is 8.73 mm, and the crack width of the trailing edge tensile fracture surface continues to increase. The crack width of the steeply inclined joint surface tensile shear failure on both sides continues to expand outward, and the bottom sliding surface tensile shear fracture penetrates. The deep rock deformation at a depth of 3.7 m below the surface reaches 0.8 mm. When overloaded to 11P, the displacement of the rear anchor plate was 22.013 mm, and the bottom sliding surface continued to expand and rupture due to tensile and shear stress. The deep rock mass below the surface of the ground had a displacement deformation of 8.5 mm, and the overall model anchorage was unstable and failed. The load displacement full process curve, tensile and shear stress distribution, and plastic zone development results revealed by numerical simulation of model anchor anchorage are in good agreement with the spatiotemporal relationship of overload rupture evolution in in-site entity model tests. [Conclusions] Under the action of overload, the deformation and failure of the model anchorage are affected and controlled by many factors including tensile shear stress state, tensile shear strength of rock mass, and joint occurrence. It is generalized into the initial tensile shear failure stage (0-1P), the tensile shear failure expansion and penetration stage (1P-7P), and the tracking joint tensile shear overall slip instability failure stage.