Abstract: Discontinuous deformation analysis (DDA) method is a newly developed numerical method and has gotten widespread attention and approval of many scholars in geotechnical engineering because of its advanced principle and numerical simulation technique. Geological model and mathematical model were established based on the damage characteristics of expansive soil cutting slope of Ningming highway. 2D model was established and theory system of the discontinuous deformation analysis method was developed. Constitutive theory of unsaturated soil was used and control constants were discussed. Then, DDA procedures were used to simulate the damage characteristics of the expansive soil slope. The results matched with the actual situation, and thus shows the procedures is rationality and effectiveness, Its results can he used for design and construction.