Based on the physical model of laboratory pull-out test,a numerical calculation model of wood bolt with the variable diameter was established by means of FLAC3D. The load transfer mechanism,the interfacial shear stress distribution,the stress field and displacement field of slurry were analyzed. The influence of anchor hole diameter,anchor diameter and anchorage length on anchoring effect were studied by the numerical simulation experiment. The results show that Q-S curve from numerical simulation is in agreement with that from laboratory pull-out test,which proves that the numerical simulation on wooden bolt pull-out process is feasible and scientific. The interfacial shear stress distribution along wood bolt with the variable diameter is uneven,and shear stress mainly concentrates among the distance of 0.1m at the top and the end of anchorage section. Structural characteristics of bolt leads to the increasing trend of shear stress near the anchor end. Furthermore,it strengthens the anchor capacity of wood bolt with comparison to regular bolt. The wood bolt with the variable diameter has the characteristics of tension-type and pressure-type bolt,and radial dilation is another feature. Compared with anchor diameter which has little impact on anchor capacity,the anchor hole diameter and anchorage length have significant influence on the pullout capacity. The formula for the ultimate pullout capacity for wood bolt with the variable diameter is proposed.