The invention discloses a method and system for automatically determining the minimum distinguishable temperature difference of an infrared imager. According to the invention, the gain of the infraredimager is maximized by placing a four-bar target in front of a standard blackbody radiation source, a standard blackbody temperature controller is controlled through a computer, and a large temperature difference value is set to enable the four-bar target to be clearly imaged; the temperature difference value of the four-bar target and the standard blackbody is gradually reduced, image data is sequentially collected, image segmentation and imaging quality analysis for the four-bar target are performed, a first temperature difference value and a second temperature difference value are respectively determined, and the minimum distinguishable temperature difference of the infrared imager is determined according to a minimum distinguishable temperature difference calculation formula. The image data of the infrared imager can be automatically collected, the working efficiency is improved, and a minimum distinguishable temperature difference result with high accuracy is obtained through clarity discrimination for the imaging quality and the space frequency corresponding to the four-bar target. Meanwhile, the image quality of the infrared imager is objectively evaluated, and the accuracyof the test result is ensured.