Abstract：Block element method(BEM) for dynamic analysis is developed and applied to historical analysis of seismic stability of rock slope. Combining the idea of viscoelastic boundary with the theory of BEM，the artificial boundary condition of BEM is formulated，which can eliminate the reflection of the seismic waves on the boundaries of the computational domain. Viscoelastic boundary has the merits of numerical stability and convenience to integrate with computational program. The inertial force of rock block is firstly computed by its acceleration obtained by dynamic analysis，then is decomposed according to supposed sliding mode into sliding force and force perpendicular to the supposed sliding direction，which is used for calculating resistance force. The factor of safety against sliding is defined by the ratio of the resistance force to the sliding force. When the seismic process finishes，the time-history curve of factor of safety against sliding of rock block can be obtained. The application of the intake slope of Xiaowan Hydropower Station demonstrates the capacity of this method.
