Abstract: To address the positional stability problem of the subreflector resulting from insufficient stiffness of its support structure for a 25 m Cassegrain antenna operating in the Q-band, an optimization design method for the subreflector support structure is proposed considering the coupling effect of the reflector rear frame. Finite element models of the subreflector support structure before and after optimization are established under different working conditions, and corresponding finite element analyses are carried out. The results show that after optimization, the first-order natural frequency of the subreflector support structure is increased from 3.31 Hz to 7.56 Hz, and the maximum deformation is reduced by 61.8% under gravitational condition. Under the boundary coupling condition, the deformation of the subreflector is decreased from 13.0 mm to 6.6 mm, and the coupling effect is suppressed by approximately 49.2%. It is verified that collaborative optimization of the stiffness of the connecting structure and the inherent stiffness of the subreflector support structure can effectively improve the overall system performance. The proposed optimization method can serve as a reference for the structural design of high-precision electronic equipment.