Simulation of infrared scenes against cold background is the key technology for the hardware-in-the-loop simulation test of a space target detection system. However, it is somewhat difficult to simulate the cold background in space with the existing technologies. A system for testing the radiation characteristics of an infrared target against cold background is established by using a high and low temperature chamber. The images of an infrared target obtained at different background temperatures are studied. Finally, the relation between the infrared target image and the background radiation is obtained. The experimental result shows that for a blackbody target with a certain temperature, the images received by the detector when the background temperature varies in a certain range have few changes. The same law can be obtained at both focal plane and defocusing plane. This conclusion is of reference value to the hardware-in-the-loop simulation of infrared scenes at lower background temperatures.