In order to improve the stability of the in-orbit electrical performance of space-borne antennas, a mechanical-electrical-thermal integrated method is proposed for the design of cable-membrane-truss antenna. The functional surface of the antenna is a Kapton membrane (or metal wire mesh) coated with a metal layer, which is fixed on the surrounding deployable truss through a tensioning cable mesh. Firstly, the coupling relationship between the mechanical characteristics of the cable-membrane-truss structure, the spatial thermal environment, and the electrical performance of the antenna reflector is studied, and a mechanical electrical thermal multi-field coupling analysis model is established. Then, with the initial pretension of the cable membrane as the design value and the minimum and maximum directional coefficient of the antenna at each position in orbit as the optimization objective, the cable-membrane-truss antenna mechanical electrical thermal integrated design optimization model was established, and a 30 meter aperture satellite antenna integrated optimization design simulation was conducted. The simulation results show that using the proposed mechanical-electrical-thermal integrated design method in this paper, the stability of the in-orbit electrical performance of the cable-membrane-truss antenna is improved by approximately 39.1%. This method can improve the stability of in-orbit electrical performance of space-borne antennas.