The group-theoretical approach analyzing the domain structure and the domain wall orientations of the ferroelastic crystal was introduced. These theoretical results were investigated by comparing them with the experimental results of several ferroelastic crystals, CsPbCl₃, Pb₃(PO₄)₂, and LiCsSO₄, which were grown by the Czochralski and solution methods, respectively. both results were agreed well and also consistent with those of previous works such s the strain method and the geometrical consideration. The group-theoretical approach showed that the ferroelastic domain walls must be the crystallographical prominent planes with fixed indices and classified by the symmetry elements characterizing the permissible domain walls. So the group-theoretical approach could be suggested as a new method for analyzing the structure of the ferroelastic domain and domain walls.