Abstract: With an example of K25 expansive soil highway landslide of G316 national highway(from Ankang to Hanyin),this paper introduced firstly geological condition of the landslide and then expounded the landslide configuration,characteristics of slip surface and slip bed,and the influence of climate,hydrological geological condition,landform and human engineering activities on this highway landslide.Unsaturated soil intensity was used to analyze particularly the formation process and mechanism of landslide and excavating was verified to be the main and direct cause of this landslide,and the results show that the course of the landslide includes five steps: excavating,unsaturated slip zone soil intenerated and shear strength decreasing or losing,slope surface upheaval and slope top crazing and shearing failure of slope foot,shearing failure area develops and connects with open crack of the back part of landslide,land-sliding formation.