Infrared thermal imager has developed rapidly in the field of military and civilian applications. How to objectively evaluate the imaging effect of the infrared thermal imager has become a problem that must be solved, which not only provides quantitative mathematical description for the imaging performance of the infrared thermal imager, but also provides the supporting basis for the study of the image sharpness, target detection distance and target tracking performance of the infrared imaging system. The imaging evaluation system of thermal infrared imager proposed in this paper has the functions of infrared image data acquisition and processing. It is used in conjunction with a target system for infrared imaging evaluation (composed of a black body, a radiation target console, a collimating optical system, and a digital display precision turntable) to test and evaluate infrared image data. The system has designed the main performance indexes, mathematical model andsteps of image evaluation. The main performance indicators including image non.uniformity(NU), signal transfer function (SiTF) , noise equivalent temperature difference (NETD), angular linearity (AL) , target imaging positioning angle error (TIPAE) and other main evaluation technical indexes. After testing, the performance of the system is very superior and it becomes the necessary debugging and testing equipment in the development of infrared thermal imager.