Infrared imaging technology has been widely used in industrial inspection. The basic principles of infrared temperature measurement are introduced. And the principle of temperature raising, the damage of high heat wasting, the factors affecting imaging temperature are also demonstrated. Testing experiments on the illminating lines at channel foreside of furnace in electric power factory are made by AGEMA570 and cooling infrared imager with focus plane array detectors. The test results of the temperature and temperature difference raised at wire joints under special working temperature and circumstance temperature are reported. Practice experiments undergoing in the factory electric devices maintenance are given.