Abstract: The working principle of a doubleblackbody measurement unit for parameters of infrared cameras is introduced. The unit employs doubleblackbody and a set of reflective infrared targets as thermoemitting sources, which makes it easy to control the temperature and temperature difference, therefore measurement reproducibility is guaranteed. The apparatus can be used for the periodic calibration of collimated irradiation of temperature difference, and to measure the parameters of infrared cameras in controllable and steadily way. A mathematic model for testing and evaluating signal transform function (SiTF) of infrared cameras was established, all the factors affecting the apparatus constant were listed in this model. Experiments were conducted to observe the effect of apparatus constants on SiTF measurement. The experiments show that the apparatus constants greatly affect SiTF measurement, temporal NETD measurement, spatial NETD measurement and 3D noise.