A method for processing negative electrode plate, comprising the following steps: arranging at least one negative electrode plate in a vacuum chamber, wherein the negative electrode plate is close to an oxygen-containing gas generator and a metal vapor generator, and wherein the side of the negative electrode plate close to the oxygen-containing gas generator is provided with a porous barrier layer; melting metal material and ejecting metal vapor by the metal vapor generator, so that the negative electrode plate is immersed in the metal vapor, wherein the ejection flow rate of the metal vapor is x ml, the density of the metal material is ρ g/cm, and the relative atomic mass of the metal material is M; ejecting oxygen-containing gas by the oxygen-containing gas generator along the porous barrier layer, wherein the ejection flow rate of the oxygen-containing gas is y ml; directly reacting the oxygen-containing gas distributed on the surface of the negative electrode plate with the metal vapor to generate a metal oxide, so that the metal oxide is plated on the surface of the negative electrode plate to form a metal oxide protective layer, wherein the molar ratio of metal atoms to oxygen atoms in the metal oxide is z, and wherein z = 22.4 · x · ρ/ (y · M), wherein the negative electrode plate comprise a negative electrode current collector, characterized in that the negative electrode plate comprise a sodium metal material formed on the surface of the negative electrode current collector, wherein the method satisfies the following characteristics: the porous barrier layer is a porous metal mesh, and the material of the porous metal mesh includes at least one of iron, titanium, tungsten, and molybdenum; the porous barrier layer has a pore size of from 40 μm to 100 μm; the distance between two adjacent holes in the porous barrier layer is from 0.1 mm to 1 mm. arranging at least one negative electrode plate in a vacuum chamber, wherein the negative electrode plate is close to an oxygen-containing gas generator and a metal vapor generator, and wherein the side of the negative electrode plate close to the oxygen-containing gas generator is provided with a porous barrier layer; melting metal material and ejecting metal vapor by the metal vapor generator, so that the negative electrode plate is immersed in the metal vapor, wherein the ejection flow rate of the metal vapor is x ml, the density of the metal material is ρ g/cm, and the relative atomic mass of the metal material is M; ejecting oxygen-containing gas by the oxygen-containing gas generator along the porous barrier layer, wherein the ejection flow rate of the oxygen-containing gas is y ml; directly reacting the oxygen-containing gas distributed on the surface of the negative electrode plate with the metal vapor to generate a metal oxide, so that the metal oxide is plated on the surface of the negative electrode plate to form a metal oxide protective layer, wherein the molar ratio of metal atoms to oxygen atoms in the metal oxide is z, and wherein z = 22.4 · x · ρ/ (y · M), wherein the negative electrode plate comprise a negative electrode current collector, characterized in that the negative electrode plate comprise a sodium metal material formed on the surface of the negative electrode current collector, wherein the method satisfies the following characteristics: the porous barrier layer is a porous metal mesh, and the material of the porous metal mesh includes at least one of iron, titanium, tungsten, and molybdenum; the porous barrier layer has a pore size of from 40 μm to 100 μm; the distance between two adjacent holes in the porous barrier layer is from 0.1 mm to 1 mm. the porous barrier layer is a porous metal mesh, and the material of the porous metal mesh includes at least one of iron, titanium, tungsten, and molybdenum; the porous barrier layer has a pore size of from 40 μm to 100 μm; the distance between two adjacent holes in the porous barrier layer is from 0.1 mm to 1 mm.