The present study investigate the effects of mechanical properties of the rock layers in the foundation of concrete gravity dam on the seismic response of gravity dam–reservoir –foundation systems. The mutual effects of different domains are considered in the present research. As a case study the biggest section of Shafarud dam in the north of Iran is modeled two dimensionally using ABAQUS software and its response to the may 1940 El–Centro California earthquake is considered.Four different ratio of elasticity modulus of foundation to the elasticity modulus of concrete of dam body are applied in the analysis obtained results show a significant effect of the foundation material properties on the crest displacement of dam and stress distribution in the dam bodywhich highlight the importance of detailed survey in order to identify the features of the site before construction.