Abstract: The infrared background simulator is an important optical remote sensing test equipment for the performance test and the radiometric calibration. Based on the simulation and the experience, a stable infrared background simulator working at 120 K low-temperature vacuum is developed, for the optical remote sensor's optical low-temperature calibration test. The infrared simulator includes the surface blackbody, the cold diaphragm and the transfer station. The temperature of the cold diaphragm is continuously adjustable in the range 90～300 K, and the temperature uniformity error is less than 3 K. The three-dimensional control accuracy of the transfer station≤10 mm. The infrared background simulator can be applied to the infrared detection performance test and the calibration test for a variety of optical sensors.