Abstract: Deep fracture is widely developed in deep rock mass of bank slopes in the deep canyon areas of western China, its engineering geological characteristics and development distribution have an important influence on the safety and stability of dam foundation rock mass.Taking the deep fracture of rock mass in the Yebatan arch dam site as the research object, we discuss causes of deep fracture by analyzing the basic characteristics of deep fracture development and engineering geological characteristics of rock mass near the arch dam.On this basis, the relationship between the development degree of deep fracture and connectivity rate of rock mass is analyzed by using the projection statistical measurement method, and the characteristics of new potential slip plane produced by rock mass joint fissure at the deep fracture zone are revealed.Based on the JRC-JCS model and the Mohr-Coulomb strength criterion, a parameter value determining method of non-penetrating sliding surface is derived, which takes into account the feature of structural plane, the strength parameters of joint fissure and rock bridge, and the compressive stress acting on the shear plane of rock mass.Finally, the typical moderate and strong deep fractures near2760m arch circle elevation are taken as an example.The influence of moderate and strong deep fractures on the stability of Yebatan arch dam is analyzed by using engineering geological stability evaluation method and finite element method.The results show that the dominant direction of deep fracture joint is roughly the same as the river trend, and its dip angle is mainly medium and steep.When the strong or medium deep fracture zone passes through unstable blocks, it can form new unstable slip body together with the structural planes such as the fault forming and sliding planes.Joint fissures in deep fracture zones with different degrees of development have significantly different effects on connectivity and mechanical indexes of rock mass.Deep fracture can weaken or block the stress transfer in rock mass.The strong and medium deep fractures in the left bank2760m elevation resistance abutment has a great influence on local deformation of the unstable body, so it is recommended to adopt grouting reinforcement or replacement treatment.