The disclosure provides a metal protective layer, sequentially comprising an organic powder coating, a high-gloss organic coating, a ductile periodic variable alloy protective film and a transparent powder coating, wherein the base powder layer is an epoxy resin or pure polyester powder coating; the high-gloss organic coating is an epoxy resin powder coating, a polyester powder coating, or a polybutadiene organic coating; the ductile periodic variable alloy protective film is formed by direct current magnetron sputtering with two targets in a high vacuum environment, and the material of the targets is composed of a Ni—Cr alloy layer and pure Cr; and the transparent powder layer is an acrylic powder coating or a polyester transparent powder coating.