Abstract: The early detection of metal corrosion under coatings can avoid damage and loss of metal structure. In this paper, the metal corrosion essence is introduced firstly. Then two kinds of metal corrosion nondestructive testing methods are provided, which are the corrosion display method and microwave detection method based on multi-function coating. These two methods can detect the corrosion degree of the metal matrix before the surface lacquer layer of the metal equipment is damaged and the metal surface is corroded. This will help to take anti-corrosion measures to the metal parts where slight corrosion has already occurred, which is important for reducing the maintenance cost of the metal equipment and improving the safety and reliability of the equipment.