This study aims to accurately detect the surface shape of large-aperture high-order aspheric mirrors. A compensation detection system is designed, and lightweight analysis of a semi-annular concave high-order aspheric mirror with inner and outer diameters of 572 mm and 800 mm, respectively, is performed. Based on the theory of three-order aberration, the aspheric mirror is compensated for and detected using the double-lens structure and single-reflecting surface, and a compensation detection system with a root-mean-square (RMS) value of 0.0037λ (λ=632.8 nm) is developed. Triangular holes are used to lighten the high-order aspheric mirror. After achieving light weight, the weight of the lens body becomes less than 30 kg, and the weight reduction rate is 32.7%. A finite element analysis of the high-order aspheric mirror and the support structure under its gravity, combined with the mechanical support structure, is conducted. The RMS values obtained when the optical axis is parallel and perpendicular to the direction of gravity are 0.012λ and 0.013λ, respectively. The maximum stresses on the mirror body and mechanical support structure are 1.308×10⁵ Pa and 1.381×10⁵ Pa, respectively. The stresses on the aspheric mirror and support structure are lower than the ultimate stress of the respective material.