Abstract: The adverse geologic elements within the dam foundation below left pedestal of the jinping I project cause not only the disruption of rock mass in integrity,but also the nonhomogeneous deformation of foundation interface,which can endanger the safety of the arc dam. Based upon their environments of rock masses qualities,the geologic defects are classified into three major classes: the anaclinal and bed-paralleled structural zone,the steep dipping and cross-bedding structural zone and the Karst fracture zone.Furthermore,the control action of the various geologic defects on the dam foundation in integrity,homogeneity,and deformation is discussed.The wave velocity and attenuation characteristic of their typical speed curves of sonic wave are also analyzed.Thereby,the qualitative evaluation of the influence degree of geologic defect to rock masses in dam foundation is made by zoning in order ofslightly,moderatelyandhighlyrates.And the conclusions emphasize that the anaclinal and bed-paralleled structural zones are large scale,and have small spacing and low wave velocity value(2500～3500m s-1) near the fault f2. The zones not only control over the shearing properties of rock masses,but also have a highly-degree influence on the differential deformation and the stress distribution of the dam foundation,which should be deal with separately.