In order to meet the requirements of lightweight and miniaturization for a new airborne opto-electronic system,the lightweight design of the primary mirror with a diameter of 445 mm in the common aperture module was carried out.Firstly,the characteristics of various lightweight forms were compared and analyzed,and the material and structure of the primary mirror were determined.Then,the relevant parameters were iteratively optimized by means of theoretical calculation and the finite element analysis aiming at lightweight ratio and the precision of face shape of the primary mirror.The mirror thickness was 68 mm,the panel thickness was 6 mm,and the rib plate thickness was 4 mm.The lightweight ratio reached at 62 % after optimization.Then,the engineering analysis of the primary mirror was carried out.Under the action of 1 g gravity,the RMS of the primary mirror was 1.13 nm when the optical axis is vertical; the RMS of the primary mirror was 0.23 nm when the optical axis is horizontal.The maximum local stress was 0.19 MPa under impact vibration.The RMS of the primary mirror was 11.67 nm under the component state.All the indexes meet the design requirements.Finally,the real primary mirror is detected by optical interferometer,and the surface accuracy RMS was 15.19 nm by measured,which verified the accuracy of lightweight design and analysis.