The electrical properties of ferrite are seriously affected by the location and shape of crack defects,but the existing detection methods can not satisfy some inspection requirements which include far distance,non-contact and visually displaying of the crack status.The detection method based on laser spot thermography will be applied to the detection of ferrite work pieces.The main idea is to analyze the temperature distribution of sample surface when the laser scan path is parallel to the crack.A new method is presented based on delayed temperature difference at symmetric points (DTDSP) to characterize the crack in the thermal image.Combined with the method of maximal temperature when the laser scan path is perpendicular to the crack,this method are used to detect the real crack of ferrite.The results show that this method can intuitively and clearly display the location and form of each direction crack.