Abstract：An extension version of discontinuous deformation analysis(DDA) is presented. In order to calculate the safety factor of a slope，the strength reduction technique is accomplished in the self-developed DDA program. In the extended DDA method，the maximal curvature of the relationship curve of the displacement and the reduced factor is proposed as the failure criterion in the slope stability analysis，which overcomes the drawbacks of the criterion of displacement dramatic increasing. And then，the stability of a rock slope during the falling of the reservoir water level is analyzed based on the failure criterion. The relationship between the safety factor of the slope stability and the speed of the falling of the reservoir water level is obtained. Finally，the excavation sequence of the high slope of Xiaowan Hydraulic Project is simulated using the program and the stability of the excavated slope is analyzed.
