In order to simulate infrared target flying process from far to near distance, a infrared target simulating system was designed, which is composed of high zoom ratio infrared continuous zoom system and large aperture projection system. The zoom ratio of continuous zoom system is 20×, the working wave-band is 8~12 μm. The large-aperture projection system has effective exit aperture of 300mm, and works under environment of -30~40℃. Based on calculation and analysis of system parameters, the material was reasonably selected and the optical power was distributed from the derived achromatic and athermal equations. Finally, the optical passive athermalized design was acquired. With dynamic optics theory, the zoom cam curve was calculated and ploted. The analysis results of system imaging quality show that the image plane is stable during the zoom process, and the imaging quality is good. The system can realize the continuous simulation of high zoom ratio target flying distance, which has advantages of of higher zoom ratio, compact design and good image quality.