The invention provides a method for quickly calibrating metal crystal faces. The crystal faces of a metal, such as copper foil, are judged by using a relationship between the thickness and the color of oxide formed on the surface of high-temperature oxidized copper, and different crystal surfaces have different oxidation rates and make an oxide film have different thicknesses, so the contrast (color) is different. The difference among different crystal faces can be clearly seen under an optical microscope. The method allows different crystal faces to be distinguished under the optical microscope through very simple operation.