Abstract: The bond between an anchor and the surrounding rock is the key factor to ensure the effectiveness of the anchorage system. To study the pull-resistance capacity of cement anchor in clay rock and the debonding mechanism of the interface under pull loads, the triaxial tests on clay rock, the direct shear tests on clay rock-cement mortar (C-C) interface, and the physical model for cement anchor pull-resistance tests are carried out. Based on the finite discrete element method (FDEM), the model for C-C binary is established, and the drawing process of cement anchor is numerically simulated. The researches show that the cohesion of clay rock is less than the tangential bond strength of the C-C interface. The internal tangent of friction angle of clay rock is larger than the friction coefficient of the C-C interface. Therefore, the shear failure of the binary gradually changes from the shear failure of clay rock to the shear debonding of the interface with the increase of the normal pressure. The bilinear cohesive model is available to simulate the failure of clay rock. The bonding interface of the binary is more suitable to be simulated by the bonding-friction model rather than the bilinear cohesive model. The failure process of cement anchor can be divided into four stages: bonding deformation stage, interface debonding stage, shear dilatancy & bite stage, and slip stage. In addition to the interface debonding, the shear failure of clay rock near the anchor is also an important factor leading to anchor failure. The bite force at the shear dilatancy stage determines the peak pull-resistance capacity of the anchor. The research results may play a guiding role in the design of anchorage structures in soft rock areas.