In the beam control system, the correction of optical axis is an essential process of the optical system. Adjusting the installation angle of the relay mirror is an effective way to change the optical axis direction. However, due to the forced deviation of the installation angle from the theoretical design value, the supporting structure will produce greater stress, which will affect the surface accuracy of the mirror. Therefore, we present an optimization method that can reduce the sensitivity of mirror surface. First, the surface sensitivity is introduced to measure the surface accuracy under the forced deflection angle. Second, the external response function of surface sensitivity is realized by combining dynamic link library and MATLAB. At last, the topological structure is optimized with the sum of the sensitivity weights of two cases as the objective function and the dynamic resonance frequency as the constraint. The optimized structure shows that the surface sensitivity around the x axis decreases from 2.58  nm  /    ±  1^″ to 0.32  nm  /    ±  1^″, and the surface sensitivity around the y axis decreases from 3.75  nm  /    ±  1^″ to 0.09  nm  /    ±  1^″.