This study determines the initial structural parameters based on the theory of coaxial three-mirror aberrations to satisfy the design requirements using a simulation software. Through the optical design concept of coaxial three mirrors, incident beam off-axis, primary mirror, and third-mirror vertex intersecting, an off-axis three-mirror optical system, which can be easily adjusted and exhibits high accuracy, is designed and combined with a digital micromirror device target generator, thereby providing a dynamic real-time simulation target for an armored vehicle. The system has a working waveband of 200--1200 nm. Further, the effective focal length is 2800 mm, the field of view is 2°, and the diameter of entrance pupil is 350 mm. The design results prove that the maximum relative distortion of the optical system is 0.1056%. Furthermore, the wave aberration of each field of view is better than λ/40 (the dominant wavelength λ=636.3 nm), and the modulation transfer function (MTF) is greater than 0.54 at 70 lp/mm, which is close to the diffraction limit. The system also exhibits a good imaging quality, satisfying the requirements of an infinite dynamic target simulation. In addition, by the analysis of the machining and assembly tolerance, the MTF of the optical system greater than 0.4 can be obtained.