The stability of the jointed rock slopes is analyzed by means of the universal distinct element code（UDEC） in which the strength reduction method is included. In the analysis

the cohesion and internal friction angle of the rock and joint plane are reduced by a reduction factor. The reduction factor becomes the factor of safety（FOS） when the slope can not reach equilibrium by decreasing the strength parameters. In addition

the slip surface and failure mode of the slope can be determined by the velocity vector of the blocks. Numerical results presented in the paper indicate that the strength reduction method combined with UDEC is reliable and powerful alternative against traditional limited equilibrium method and that it will be a new approach to obtaining the slip surface and FOS of jointed rock slope.