Abstract: To achieve the lightweight design of the subreflector support structures for a spaceborne antenna, several typical support structure models are built using finite element method. The effects of the outer diameter, thickness of the bar cross section and the axial angle between the bar and the antenna on the natural frequency of support structures are analyzed first. Then the bearing area of the subreflector is optimized using topology optimization technique with natural frequency as constraints and the minimum mass of the bearing area as target. Results indicate that the six-bar model can obtain the highest natural frequency value under the same structural mass. The natural frequency increases with the increase of the axial angle between the bar and antenna first, and then decreases gradually in both the three-bar model and the four-bar model. However, the natural frequency decreases with the increase of the axial angle between the bar and antenna in the six-bar model. The mass of the optimized subreflector is reduced by about 75.28% compared with theinitial state.