Based on application scenarios of infrared target simulator dynamic calibration system, the design characteristics of the optical system in dynamic calibration system were analyzed, then it was pointed out that the optical system should select the refraction-reflective secondary imaging optical structure. Based on the classical optics athermal principle, refraction-reflective system athermal methods was refined by calculating then matching the optics and machine material precisely. By the method, a optical system with F/2, focal length of 370 mm, working band of 3.7 to 4.2 ?滋m, total length of 182 mm was designed. The optical system selected 512×512, 15 ?滋m×15 ?滋m specification Stirling refrigeration detector, and imaging quality in the -40-60 ℃ was close to the diffraction limit. The ghost and Narcissus analysis models were established, the results show that the optical system has strong ability to suppress stray light and others excellent performance. The optical system satisfies the requirement of dynamic calibration system of infrared target simulator used in complex harsh environment.