Stereographic projection classifies failure modes of slopes in a jointed rock mass by the joint set distribution characterization, and limit equilibrium method calculates the safety factor of the slopes using ground parameters. However, the former is qualitative and the other is only applicable to typical models, so it is difficult to apply them on the field rock slope without other complement like numerical analyses. In this study, the movement of slope was described with $PFC^{2D}$, one of the discrete element methods using the working effect between particles. Results were compared to those of analytical ones. The result of stability evaluation was similar to each other, and the failure points of the unstable slope and plane failure aspect were found. These results showed that DEM analysis with stability evaluation and failure pattern determination can be a good tool to describe the behavior of slope failure.