To satisfy the requirements of high stiffness and low inertia of the center section of a large aperture telescope， a lightweight center section is designed. Further， because the traditional method cannot detect the geometric tolerance of the center section， an optical detection method based on an autocollimator and laser tracker is proposed. According to the requirements of the overall structure of the telescope， the size range of the center section is determined， and the transmission path of the force is analyzed. The topology optimization analysis and structure design are carried out using the variable density method to minimize strain energy. Based on the angle measurement principle of the autocollimator， the reflecting mirror is placed on the face of the center section hole to measure the parallelism error of the face on both sides. Based on the position measurement principle of the laser tracker， a high-precision turntable is used to find the central point of the center section hole. Then， the central point coordinates of holes on both sides are measured， and the coaxiality error is measured. Compared with the center section designed by traditional means， the mass of the center section designed under the guidance of topology optimization is reduced by 21.5%， and the static stiffness is increased by 14.3%. The parallelism error of the faces of the holes on both sides of the center section detected by the optical method is 0.016 mm， and the concentric error of the holes on both sides is 0.03 mm. The center section designed by topology optimization has obvious advantages in improving stiffness and reducing inertia. The detection of geometric tolerance of the center section can be realized by using the proposed optical detection method， which solves the detection problems in processing.