This paper employs an organized methodology to find the optimum shape of arch dams. In order to create the geometry of arch dams a new algorithm based on Hermit Splines is proposed. A finite element based shape design sensitivity involving body force, hydrostatic pressure and earthquake loadings is accomplished. The sensitivity analysis is represented using the concept of mesh design velocity. The cost of sensitivity analysis in this paper is about (3%) of the cost of the forward or backward finite deference based gradient calculation methods. Moreover, the accuracy of the derivatives in the finite difference methods depends on the perturbation of the design variables (ΔXi), whereas in this paper the accuracy of sensitivities is independent of perturbation values. In the optimization model, many geometrical and behavioral constrains are included in the model in comparison with previous researches.