In order to investigate the effects of concrete plug treatment on the stress distribution in rock foundation of gravity dam, the authors carry out the gravity dam modeling tests in consideration of the location of a fault and the depth of plug. Based on the experimental results, it is confirmed that the stress distribution is largely affected by the location of a fault and the depth of plug. The effects of plug installation are 1) to enlarge the area of dam base and to distribute the concentrated force from dam body, and 2) to restrict the deformation of the foundation around the fault and to normalize the stress distribution. The stability of foundation models is examined by shear friction factor and the calculated results are compared with the model test results.