Abstract: The space-borne phased array antenna is developing towards large aperture, high heat consumption, high integration and strict parameters, but the increase of its structural size, array scale and weight conflicts with strict lightweight requirement. A comprehensive lightweight design method is proposed in this paper, which includes replacing traditional metal structures with carbon fiber composite and aluminum honeycomb sandwich panels to reduce weight through material optimization, optimizing structural layout based on mechanical simulations (modal and random vibration analysis), combined with orthogonal distribution of functional components to enhance overall stiffness and validating the design effectiveness through mechanical experiments. Results show that with the proposed method the weight of the bearing structure is reduced by 50% at least, the fundamental frequency is increased from 50.3 Hz to 130.1 Hz, and thus the mechanical requirements of space-borne equipment is satisfied. This method provides a systematic solution to lightweight design of large-aperture space-borne antennas.