Bedding rock slopes widely exist in the construction of hydro-junctions， which stabilities are affected by weak planes like joints. In general， the bedding rock slopes are reinforced by bolts， and it is of great importance to study the reinforcement mechanism when it comes to the design and construction of bolts. Firstly， the contact model considering the bond size was implanted into a distinct element method （DEM） software PFC2D to establish the model for the bedding rock slope， where three sets of bolts with different lengths were introduced to form the model for the reinforced slope. Then， the failure processes of the unreinforced and reinforced slops were simulated with the gravity increase method. Finally， the reinforcement effect and mechanism of the slope by bolts were analyzed by comparing the safety factors， failure patterns and force chains distributions of the unreinforced and reinforced slopes during the failure processes. The results show that the slope safety factor obviously becomes larger in the reinforced slope， and thus the stability is improved and the reinforcement effect is obvious. Compared with the unreinforced slope， the failure pattern of the reinforced slope stays unchanged.However， more time is needed for the failure to occur， the sliding surface is shallower and the amount of slip masses is smaller. The bolts improve the stress state of the slope，and in the unreinforced slope， the tensile and compressive forces concentrate on the rock bridges， while in the reinforced slope， the bolts holds most of the tensile forces and the rock bridges basically only resist the compressive forces.