Abstract: In this paper, we mainly describe the research results of the engineering characteristics of expansive soil, and the deformation and failure mechanism of the expansive soil slope. Relying on the survey and research of the middle route of the South to North Water Transfer Project for more than half a century, with the projects of the National Science and Technology Support Program, we studied through field investigation and laboratory experiment, developed a lot of tests include slope monitoring, field anatomy and numerical value simulation in the large prototype channel, and researched the engineering characteristics of expansive soil structure and slope failure characteristics. The results show that the expansive soil has obvious vertical zoning characteristics in the macro structure. The failure of the shallow layer is mainly on the slope erosion and shallow surface creep. The deep sliding failure is affected by the internal structure surface of the expansive soil, and the strength of the soil slope depends on the strength of the weak structure surface. Based on the experimental research results, we proposes a new failure mechanism of shallow creep and deep broken line sliding failure of expansive soil.