For the optical components in the optical system, it is not only required to have good optical transmittance, but also to achieve the shielding of the electromagnetic wave band. Traditional metal materials suppress the light transmission performance while shielding electromagnetic waves. Carbon-based materials have become the first choice for mesh structure shielding materials due to their special physical and chemical properties and excellent electromagnetic shielding properties.In this paper, the copper metal plane structure is designed as a mesh structure, and a graphene layer is added to the copper mesh structure to establish a multi-layer copper-based graphene composite mesh structure model. In the range of 12~18 GHz electromagnetic frequency band, HFSS simulation software is used to simulate the electromagnetic shielding effectiveness of copper-based graphene multilayer composite mesh structure model by waveguide method. The linewidth parameters of the basic mesh structure are changed, and the electromagnetic shielding characteristics are simulated and experimentally studied. The absorption loss SEA and reflection loss SER of different structures are calculated to further explore the electromagnetic shielding mechanism of the new structure.The results show that in this electromagnetic frequency range, with the increase of electromagnetic wave test frequency, the electromagnetic shielding effectiveness SE of all structures shows a downward trend. When the same structure is at low frequency of electromagnetic wave, the shielding material has relatively poor permeability and propagation ability to electromagnetic wave, strong blocking ability to electromagnetic wave, and high electromagnetic shielding effectiveness SE. The electromagnetic shielding effectiveness of the three copper-based graphene multilayer composite mesh structures is improved compared to the single copper mesh structure. Among them, the double-sided superimposed graphene layer structure in the copper mesh structure is the best structure of the electromagnetic shielding effect in the three composite structures compared with the copper mesh structure. The relationship between the electromagnetic shielding effectiveness of the three composite structures is consistent with the theoretical calculation. The electromagnetic shielding effectiveness of this structure with double-sided graphene layer is more than 1.7 dB higher than that of a single copper mesh structure, and the absorption loss of electromagnetic wave is increased by 4.81 dB. Due to the superposition of graphene layers in the three composite structures, the absorption of electromagnetic waves by graphene is increased, so that the overall structure has a certain absorption effect on electromagnetic waves. While improving the overall electromagnetic shielding effectiveness of the structure, the composite structure also significantly improves the absorption loss of electromagnetic waves. Under the same electromagnetic frequency range, when the material properties of the composite structure and the mesh period are constant, the line width parameters of the basic mesh structure are changed. With the increase of the mesh line width, the electromagnetic shielding effectiveness of the composite structure is also increasing, while the mesh transmittance is decreasing. It is concluded that for the mesh substrate structure, there is a mutually restrictive relationship between electromagnetic shielding effectiveness and light transmittance.The electromagnetic shielding characteristics of three kinds of multi-layer composite structure samples designed by simulation are tested to verify the accuracy and feasibility of the simulation in this study. The experimental results show that the electromagnetic shielding effectiveness of the three multi-layer composite structure model samples is higher than that of the copper mesh structure model samples. The experimental results are almost consistent with the simulation and theoretical calculations, and the trend of the electromagnetic shielding effectiveness curve is consistent, which further verifies the feasibility of the simulation and the accuracy of the data results. The results of this study have certain reference value and reference significance for improving the electromagnetic shielding characteristics of metal materials and the electromagnetic shielding characteristics of metal and non-metal composite structures.