For choosing the value of deformation modulus reasonably during optimally designing an arch dam, several arch dams with different height which supported by rock bases with various deformation modulus were optimized, and the rough value which was required by arch dams with different height and it’s variation law were obtained. The law could be referenced by other engineers who want to optimal design an arch dam. At the same time, the stress of an arch dam which was hold by rock bases with different deformation modulus was analyzed. It was concluded that the arch dam will not be more safety when small value of deformation modulus is chosen, and the value of an arch dam’s body stress should less than the tolerable value in case that the deformation modulus of the rock will change.
