It is necessary to test and analyze the distortion of an infrared imaging system in a laboratory because the ability of the system to play a role on the platform is dependent on the distortion control of an infrared imaging system. We have proposed a method based on a test of sub-pixel precision and precise angle measurement to calculate distortion using centroid difference data. It is laborious to test the distortion of an infrared system with a large field of view using a method which requires the computation of a large number of coordinates of points. Furthermore, the location of the field view could be a problem for the partial distortion method. By using the proposed method, the aforementioned problems can be addressed. We applied the method to evaluate a thermal system and the results were in agreement with those of the simulation software. The error control was less than 0.02%, which can meet the requirement. Moreover, the performance of the system was evaluated to analyze how the distortion affects the ability of the system.