Mathematical expression of vibration deterioration effect of structural plane is obtained by experiments;and then the expression is applied to rock slope?s dynamic stability analysis. 3DEC is selected as calculation engine,and at each dynamic calculation step,mechanical parameters of structural plane are refreshed according to the real-time values of dynamic response;meanwhile,the earthquake inertial force at that moment is obtained via net vectorial nodal force?s vector calculating. Hence the rock slope?s instantaneous safety factor is obtained based on the limit equilibrium theory. Therefore,the time series of factor of safety can be got for whole earthquake process by dynamic calculating;and the dynamic stability evaluation index is determined by minimum average safety factor method. Consequently a new method for analyzing dynamic stability of rock slope is presented,which takes vibration deterioration of structural plane into account. Finally,the method is used to study a rock slope case in Wenchuan earthquake-affected region;and the analytical results matched actual geological survey situation well,so as to testify the feasibility and correctness of the proposed method.