Abstract: Based on the surface impedance model of metal mesh and the full wave simulation software, in this article the applicable range of the formula for calculating the shielding effectiveness of metal mesh for plane wave is discussed.On this basis, when the shape of metal mesh is diamond, the shielding effectiveness of the metal mesh is calculated by using the full-wave simulation software, and then the mechanism of the wire mesh is analyzed. According to transmission line theory and the surface impedance of metal mesh, the transmission line model is equivalent to double-layer infinite metal mesh, and an analytical model for calculating shielding effectiveness of double-layer infinite metal mesh is proposed. Furthermore, shielding characteristics of the double-layer metal mesh and the difference between the single-layer metal mesh and the double-layer metal mesh are discussed.