Due to importance and application of arches in historical structures, arch shape optimization has been discussed. The objective of this study is to determine brick masonry arches under dynamic loads. In this paper, considerable attention is given to arches, their importance, modeling stages, dynamic analysis and arch optimization using ANSYS 11 software. A multiple stage analysis framework was conducted for semicircular arch: 1- The study of optimum shape for semicircular arch on the base of minimize of arch weight. 2- Determination of linear and nonlinear analysis limits by increase of density. 3- The study of optimum shape in semicircular arch by linear and nonlinear analysis. All of these stages have been conducted for obtuse angel arches,(steep, normal and diminished), four- centered pointed arch, tudor arch, ogee arch, equilateral arch, catenary arch, lancet arch, four-centered arch (normal, diminished and steep) The main purpose has been study of arch optimum shape in three spans (4, 5 and 6m) for minimize of weight: Finally, according to the results, the optimum shape in arches under dynamic load has been determined.