Abstract: The passive and active infrared thermal imaging technologies were analyzed based on the Stephen-Boltzmann law（W=εσT4）. The passive infrared imaging technology adopts a thermal camera to receive the infrared radiation of an object, and the active infrared imaging technology, based on the equation of heat exchange, researches the interaction of variation thermal sources with medium material and geometrical structure. The active infrared imaging technology obtains the information of material homogeneity and the structure under its surface to implement the non-destructive testing and inspection by monitoring the temperature variation of material surface through flashing light, ultrasonic wave, laser, THz wave, hot blast, electric current or mechanical vibration. The applications of both technologies are compared according to their principles.