Abstract: According to the requirements of design specifications for standard dynamic target generator of space，we improved the Cassegrain RC system，namely joining a hyperboloidal mirror between the second lens and image plane. The optical system can collimate the output from liquid crystal light valve in 0.4 μm~0.7 μm and 8 μm~12 μm，and enable an image system to be tested out of 1° field of view. The effective focal length is 1 600 mm and the relative effective aperture is F/1.2 .The result indicates that the diffuse plaque rootmeansquare(RMS) is less than 0.5,the modulation transfer function (MTF)of the coaxial threemirror system values is always greater than 0.7,and close to the diffraction limit at the corresponding spatial frequency of visible and farinfrared band,hence the coaxial threemirror system meets the requirements of image quality.