Aiming at the feasibility of the damage recognition of AGS, the modal curvature difference method is used to evaluate the damage factors of the structure. The regular triangular grid structure is analyzed using the finite element method in ANSYS, the modal curvature difference between the original structure and the damaged is calculated by using the modal displacement which is got from the finite element analysis, and the damage can be recognized through this label. The result shows that: the first modal curvature difference is sensitively to the damage of the ribs for single damage and the first three modal curvatures should be analyzed for multi damages.