The system is based on an RC structure to measure the optical characteristics of small targets and space targets. The initial structure of the reflective optical system was established by calculating the curve equation and the Gaussian formula. The re-imaging relay lens group was introduced into the structure of the system to realize the optimal design, which solves the problem of 100% cold diaphragm efficiency. The imaging quality was evaluated using Zemax, and a system with a focal length of 380 mm and a diameter of 200 mm is not only compact and simple, it also meets the actual measurement requirements.