It was difficult to analyze the stability of the rock slope for its complex geological structure. Rock mass was the geological body that subjected to intense deformation and suffered damage, which was composed by rock and jointed rock mass. When the rock mass was in the high steep rock, its loading state was further complicated. First we analyzed the failure mechanism of jointed rock mass in theory, and we used Flac3d with the Mohr-Coulomb yield criterion to simulate the displacements and stresses. We built three models that included angles with level line were 25°, 45° and 65°. The results showed that, all around the joints stresses concentration occurred, the maximum compressive stress occurred at the crack tip; the final crack direction always tended to the direction of maximum compressive stress; and when the angle was bigger, before the crack expended further, the strength of rock decreased first, and destroyed first.