Under the action of engineering load and seepage pressure, thestrength and deformation parameters of dam base rock insluice engineeringis easy to be weakened. This is adverse to the safe construction and theprojectoperation. In the Datengxia sluice damproject, considering that the unfavorable foundation geological conditions such as the multi-layer monoclinerock stratum, the large and density weak interlayer, etc., the sliding failure mode of foundation needs to be further studied. In this paper, the comprehensivegeomechanical model is adopted and the failure test is conductedto research the overall stability of dam and foundation fora typical dam section. By means of overloading methodand strength reduction method, the displacement characteristics of dam foundation during the whole period of normal condition, strength reduction and overloading are obtained. And the failure process and failure pattern of dam and foundation are revealed as well.The results show that the displacement of dam foundation in the period of strength reduction and overloadingis greater than that of normal condition.Particularly, the deformation of the shallowweak interlayer is more obvious. As the overload factor increases, these shallow parts of the weak structural planes R9, R14, R17, and R19 gradually crack. Finally, the failure mode presents the trend of sliding instability along the foundation surface. It indicates that these shallowstructural planes play a controlling role in the deformation and stability of dam and foundation in this project.