Abstract: In order to study the deformation behavior of contact clay of an ultra-high core dam, 4 groups of centrifugal model tests are carried out. The results show that the differential deformations among the contact clay, bank and core wall are acceptable, and no separation are observed at contact parts. The deformations of the contact clay caused by vertical loads include the compression deformations vertical to the bank and the shear ones parallel to the bank. The contact clay is in the compression-shear state. The compression and shear deformations both increase with the loads in a log-linear trend. This trend is greater at steeper bank slope. The deformation development of the contact clay gradually becomes stable after construction.