Abstract:According to the experiments and research and the engineering practices,the paper summarizes the geologic characteristics of early tertiary expansive rock,i.e. expansivetcata- clastic and low strength along the Nanning-Kunming Railway in Baise Basin of the Guangxi Province,and analyses the harm of these characteristics to the cut slope engineering and the rule of deformation of the cut slope of the expansive rock. By comparison,the design and con-structing principles of the cut slope engineering of the expansive rock are recommended。