Abstract: Method of preparing cadmium coating metallographic specimen dopted the conventional metallognaphic preparation method for cadmium coating on the surface of the stainless steel matrix,it can make the cadmium coating sunken and make it become black.Pracietice shows,if you master the method and skill in the process of preparing specimen,such as specimen inlay,grippping,grinding and polishing,you can prevent the cadmiun coating sunken and measure the thickness of the cadmiun coating perfeetly.