For the requirements of the infrared imaging system performance testing and evaluation applications, an athermalized mid-wave infrared scene projector was designed, based on Digital Micro-mirror Device(DMD). The aberration and design method of the optical system for infrared scene projector were analyzed, and the athermalization for the scene projector was also discussed. A splitting lens and a compensation lens were used to address the light splitting and aberration balancing problems in the illumination of the telecentric projection systems with a large relative aperture. So the resolution and uniformity were improved, and the field of view was increased. The optical system is composed of a telecentric projection lens and a Kohler illumination lens with tilted image plane. The optical passive athermalization method was introduced into the design, which improved the stability of the system. The spectral band of the system is 3～5 μm , the focal length is 255 mm with a F/2.6 relative aperture, the field of view is 5.1°, and the exit pupil distance is 200 mm. The image quality of the system approaches diffraction limit with MTF>0.6 at spatial frequency 17 lp/mm in the whole operating temperature range of －20 ℃~ 60 ℃. The proposed athermalized mial-wave infrared scene projector has the advantages of high resolution, excellent uniformity, compact size and low weight.