The invention discloses a method and a device for in-situ growth of a polycrystalline graphene anti-corrosive film on a metal surface. By providing a reactor with one opened end, a liquid-state carbonsource is heated by electromagnetic induction in a normal pressure environment to realize fast growth of polycrystalline graphene on the metal surface, and large-area fast preparation of a graphene film on the metal surface can be conveniently realized. The prepared polycrystalline graphene film can effectively prevent permeation of ions such as water vapor, oxygen gas and acid radicals, therebygreatly improving the chemical corrosion resistance of the metal, greatly prolonging the service life of the metal, and solving the problems of complicated preparation processes of an anti-corrosive coating and combination of the film and the metal surface. In addition, a growing ultra-thin polycrystalline graphene coating has no great influence on the properties of the metal.