In order to investigate the failure mechanism of slopes with different types of joints, the contact model considering the bond size was implanted into the distinct element method(DEM) software. Based on the gravity increasing method, the failure processes were simulated, and the slope configuration, the distribution of bond breakage, and the movement of slip masses were analyzed. The results show that the sliding surface is formed from the failure of coplanar joint in the bedding rock slope, while the noncoplanar joint in the toppling rock slope. The toe of the slope is a weak area in both the bedding and toppling rock slope. Besides, the mid area near the slope surface in the bedding rock slope as well as the slope shoulder area in the toppling rock slope are flimsy. In addition, the DEM simulation is able to evaluate the stability of the slope like the limit equilibrium methods and better reflect the forces among rock fragments and the gradual failure process.