In this paper, we present the approaches of applying Discontinuous Deformation Analysis (DDA), a powerful numerical method, to practical problems related to slope stability analysis in three aspects: 1) calculation of factor of safety, 2) simulation of failure process and 3) rock fall analysis. The theory and the mechanism of modeling rock failure in DDA is briefly introduced. The factor of safety is directly defined based on the failure mechanism and is easily to be obtained in DDA calculation. Two practical applications have been presented to show how to use the method in practice. One application is the simulation of a slope rock mass collapse happened in Hokkaido, Japan. The other is rock fall simulation of a slope located in Niigata, Japan. It has been shown from two practical applications that DDA is a very effective numerical method for slope stability analysis.