The accurate testing of electromagnetic parameters for foam absorptive materials presents a significant challenge. In this study, we developed an electromagnetic parameter (complex permittivity) characterization method based on the reflectivity calculation theory. By establishing a relationship between the electromagnetic parameters and reflectivity, we achieved precise characterization of the foam absorptive material’s electromagnetic properties. We propose a measurement system using the arcuate method, where the reflectivity for both vertical and horizontal polarizations is measured at different incident angles. The inversion problem is solved using the Newton-Raphson iteration algorithm. This approach only requires the amplitude of the reflectivity, thus eliminating the impact of phase errors. The proposed testing and characterization method only needs a single sample without the need for precise cutting, preserving the microstructure of the foam absorptive material and minimizing the influence of processing errors. To validate the proposed testing scheme and algorithm, experiments were conducted in the frequency range of 8 GHz to 12 GHz, and the results were compared with those obtained using the classic waveguide method (NRW). The experimental results demonstrate that the theoretical reflectivity values for expanded polypropylene (EPP) at different thicknesses and angles match well with the measured values. Except for resonance points, the deviation between the theoretical and measured values ranges from 0.087 dB to 0.806 dB, which meets the arcuate method testing requirement (±1 dB), thereby verifying the feasibility and effectiveness of the proposed electromagnetic parameter extraction algorithm.