Abstract: Based on the Ritchey-Chretien(R-C) system, a refractive/reflective system with a Margin-like mirror and 3 correcting lenses in front of the focal plane was designed with the help of Zemax software. It has a focal length of 3000mm, F number of 8, waveband of 450nm~900nm, and the field of view reaches 1. It is shown that the value of modulation transfer function(MTF) is higher than 0.55 at 50 lp/mm, the image quality reaches the diffraction limit,and the distortion is less than 0.022%. An R-C optical system is made up of the aspheric mirror of the Margin-like mirror and the primary mirror of the system without the spherical aberration and the coma aberration. The refractive surface of the Margin-like mirror shares the optical power of the secondary mirror, reducing the asphericity of the aspheric mirror. Results show that the Margin-like mirror can lessen the square asphericity of the secondary mirror from 4.356 to 1.940, and reduce the length of the system from 600 mm to 550 mm.