Abstract: In order to cope with the threat of electromagnetic radiation in urban building spaces, the influence law of multi-layer graphene (MG) and expanded polystyrene (EPS) spherical particles on the electromagnetic absorption properties of cementitious composites was investigated. The optimal combination of EPS-MG-cement-based composite wave-absorbing materials with double-layer flat plate structure was explored, and the mechanism of wave-absorbing action of the composites was elaborated. The experimental results showed that the EPS particles in the composites form a unique porous array structure in the matrix, which significantly enhances the electromagnetic matching performance between the material and the free space. Moreover, the EPS spherical particles are both wave-transparent agents and resonance cavities, which can form a good porous conductive network with MG under reasonable doping, and can absorb the energy of the incident electromagnetic wave through interfacial polarization, resistive loss and polarization relaxation. On this basis, this paper makes full use of the density gradient and interlayer effect through the double-layer flat plate combination structure, which further improves the dissipation of electromagnetic wave energy in the transmission process, realizes a good synergistic enhancement effect between the structure and the material components, and the effective absorption bandwidth of 2~18 GHz reaches 7.93 GHz. The maximum absorption peak of −18.80 dB is obtained, which has a good electromagnetic wave absorbing performance, and provides a new idea for the development of wave-absorbing materials for low-cost buildings.