Abstract: The testing of the imaging parameter minimum resolvable temperature difference (MRTD) for infrared thermal imager was studied. Firstly, the testing method and device of the MRTD as well as the working principle of the evaluation system for infrared thermal imager were introduced. Then, in the process of MRTD testing, the influence of the testing position, differential blackbody temperature difference, differential blackbody emissivity and optical system geometrical aberration of infrared thermal imager on the testing results was analyzed in detail. Aiming at these problems, a method of calibrating the temperature difference of the infrared thermal imager evaluation system by using the infrared scanning radiometer was proposed. This method was used to test the MRTD of the infrared thermal imager at a certain spatial frequency, and the testing results were given to provide a reference for the MRTD parameters accurate testing of the infrared thermal imager.