Abstract: Fatigue damage is one of the main failure mode of engineeringstructure and machinery, so it is important to determine the fatigue limit ofmaterials. This paper, based on fatigue energy theory, discusses the principle thatmaterials' fatigue limit can be determined by thermographic method. The fatigue test of a steel specimen with rectangular sectionis carried out using infrared thermal sensor, and the variation oftemperature on the specimen is recorded during the fatigue test, and the fatigue limit of the material is then evaluated. Theexperiment indicates that the infrared thermographic technique candetermine the fatigue limit of materials fast and accurately, and this methodenjoys reliability, economy and convenience.