Abstarct: Dynamic analysis of arch dams is continously improving. Numerical models of arch dams is advancing both by progress of computers and methods of analysis. Absorption of earthquake waves at boundaries is one of the factors which have influence on dynamic analysis of arch dams. Vibrations and pressure changes in each point of water behind dam, is propagated with sound speed and hits the boundaries. At boundaries some part of this wave is absorbed and some part of it is reflected into the domain again. The aim of this research is to study influence of absorption of acoustic waves at boundaries on the results of analysis. For this purpose double curvature arch dams are studied by different forms arch dam with and without contraction joints and with linear and non-linear models. In all cases it was observed that absorption of waves at boundaries decreases the force due to earthquake.