Loading transfer mechanism of anchorages is essential in controlling the supporting ability of a fully-grouted rebar. Considering the complexity of loading transfer between rock and rockbolt, the shearing behavior along the bolt and the cementation materials is examined in laboratory. The results showed that the peak/residual shear strength and shear stiffness were increasing with the increases of mortar strength or normal stress. Besides, the increase of shearing load ratio would increase the peak shear strength and shear stiffness, but had less influence on the residual shear strength. By simplifying the shear stress versus slip distance curve into trilinear bond-slip model, the debonding at the anchorage could be expressed in three stages, such as strengthen, soften, and slipping. Numerical simulations on the crack initiations and propagations at the interface were carried out using DDA. The results illustrated that the tensile damage was the major failure mode at the initial loading, followed by tensile-shear mixing modes near the peak value. After that, the shear behaviors were associated with the friction and the shape of the particles. By introducing the tri-linear bond slip features into the fully-grouted rebar model to simulate the coupling at anchorages, the results showed the deformability of the rebar would be much reduced when the ratio of pullout loading was higher.