This paper describes the optical design of a high-resolution spherical grating monochromator beamline being constructed in National Synchrotron Radiation Laboratory at University of Science and Technology of China. The beamline consists of a spherical grating monochromator with two including angles

a pre-focusing mirror system composed of a horizontal deflection plane mirror and a vertical focusing cylindrical mirror

and a post-focusing toroidal mirror. It has high resolution power and high photon flux over the designed energy range. Results of optical raytracing are also presented.