Aiming at the needs of remote infrared target detection, for improving the detection ability of optical system in a complex environment, the cooled common path infrared dual-band refractive-diffractive telephoto objective is designed. The working wave-band of the telephoto objective covers the infrared medium-wave (3~5 μm) and infrared long-wave (8~12 μm). A transmission common path structure is used in this telephoto objective. The telephoto objective consists of objective and relay lens. The focal length of the telephoto objective is -200 mm, the F number is 2.8, and the full field of view is 3.2°. The detector adopted is HgCdTe mid-wave infrared focal plane array of 2/3 inch (1 inch=25.4 mm). Its resolution is 320 pixel×256 pixel and pixel size is 30 μm. The image quality of this telephoto objective is prefect. At cut-off frequency of 17 lp/mm, the modulation transfer function (MTF) of the infrared medium-wave is greater than 0.5 for each field of view, and the MTF of the infrared long-wave is greater than 0.3 for each field of view. The root mean square radius of spot diagram for the each field of view is much smaller than Airy disk radius. The cold shield efficiency is 100%. This infrared telephoto objective can be used in the observation-aiming system of the tank.