Abstract: Unstable rock mass is a typical kind of hazard geological body. Its formation, deformation and damage are controlled by the geological environmental conditions. Geological basic elements play a decisive role in the disaster-pregnant process. The relationship between geological basic elements and the formation of the disaster is the key issue in the study of the deformation regularity and failure mechanism of the unstable rock mass. The authors made an analysis of such relationship on the basis of the regional geological tectonism, the Hengshixi anticline structure, the development of geological structural planes, the lithologic combination and the engineering geological conditions, in conjuction with the unstable rock mass deformation and failure process. The researches show that the Hengshixi anticline structure that bred the Wangxia unstable rock mass was formed at the uplift stage in Indo-Chinese epoch. The fold appearance was formed mainly in Yanshanian, and later gave way to inheritance transformation. The unstable rock mass was formed mainly in the arch core area, particularly the hinge position of the fold. The five kinds of critical cracks that controlled the deformation of the rock mass had close relationship with the"V"-shaped cracks at the top of the rock. The brittle rock at the top of the anticline was affected by strong tensile splitting under the influence of buckle fold effect and the superposition of the stepladder interlayer-gliding effect. As a result, the tensile cracks almost parallel to the axial surface of fold were formed. Groups of geological structural planes were developed in the Wangxia unstable rock mass. The primary structural plane provides background for every critical crack and block, controls the scale, range and strength of the deformation, and also governs the deformation critical parts, especially the location, traction sections and intensity of the frontal weak layer. The tectonical plane mainly controls the extension direction, distance and style of the critical cracks, as well as the deformation direction, the cracking range and scale, the fall-block and split position of the critical blocks; it also governs the unstable rock mass at the bottom of the critical parts in such aspects as the location of pressure tension crack, the opening degree and the displacement direction. The secondary plane mainly controls the deformation at the back edge area, the inheritance deformation of the critical cracks and the expansion of the critical block, thus playing an important role in the formation of cracking damage of the unstable rock mass. In addition, the stratigraphic lithology of the Wangxia unstable rock mass constitutes a typical hard-soft-hard lithologic combination, and provides geological structural combination condition for the deformation of the rock. The large mined-out area at the bottom controls the overall slump deformation of the unstable rock mass.