Abstract: As a typical geological defect in Yebatan hydropower dam site area,the impact of multi-faults on the deformation and anti-slip stability of the high arch dam base cannot be ignored. Based on the development and distribution of faults in the dam area and their basic characteristics,this paper proposes the concept of multiple faults,and analyzes the geomechanical formation mechanism and spatial distribution characteristics of multiple faults in the foundation rock from the perspective of dynamic kinematics. It comes up with three basic combination patterns of multiple faults in the Yebatan hydropower dam site area. They are the parallel arrangement type,the conjugate shear type,and the primary & secondary intergrowth type,which simplifies the complex fault situation in the foundation rock. The combination of qualitative and quantitative methods is used to compare and analyze the degradation degree of faults on the quality of the foundation rock under different combination patterns. The degradation degree of the conjugate shear type and the primary & secondary intergrowth type is stronger,which degrades the quality of the rock body by one grade. The degradation degree of the parallel arrangement type is more general,which degrades the quality of the rock body by half grade. The relationship between the influence path of faults and the degradation degree under different patterns is discussed. The research results provide technical support for the excavation treatment and risk prevention and control of the foundation rock of Yebatan Hydropower Station.