Abstract: Considering the importance of the effect of concrete arch dam body strength on their seismic performance, this research evaluated the effect of Young Modulus of both the body concrete and foundation as strength parameters and examines the responses to achieve the optimal body stiffness using probabilistic and uncertainty method. The ANSYS software was used to complete the finite element analysis of the dam-reservoir-foundation system and the Monte Carlo method, which is a new method for parametric study and sensitivity analysis, was used for uncertainty analysis. For seismic analysis, the horizontal and vertical components of Northridge, San Fernando and El Centro earthquakes are separately applied in 3d directions. The earthquake components were scaled to the maximum credible level of ground motion acceleration. The foundation rock is simulated using a massless foundation model and dam-reservoir-foundation interaction is considered for seismic analysis of system. The results show the effect of the modulus of elasticity of the concrete which is directly related to the stiffness of the system. The results indicate the effect of the dam body concrete stiffness on the responses. According to the design criteria, it is possible to investigate the safety status of the dam and select the optimal state in terms of structural strength for the model. However, in order to properly select the modulus of elasticity of the concrete of the dam body, it is necessary to consider the simultaneous effect of the stiffness of the foundation and to select the optimal value.