Absorbing materials are an effective supplementto external stealth technology. After electromagnetic waves enter the interior of absorbing materials, they should be rapidly and maximally attenuated. Therefore, when we design the electromagnetic parameters of absorbing materials, impedance matching should be considered to maximize the entry of electromagnetic waves into the material. On the other hand, it is necessary to ensure that all electromagnetic waves entering the material are attenuated as much as possible. For absorbing materials, it means that the material must have a large imaginary part of the dielectric constant and magnetic permeability, which can cause attenuation of electromagnetic wave energy. Traditional microwave-absorbing materials mainly focus on microwaves. With the development of technology, terahertz radar has been put into use. It is necessary to study and explore whether traditional microwave absorbing materials can effectively attenuate in the terahertz and even infrared frequency bands and evaluate these absorbing materials in the terahertz frequency band. Two types of absorbing material plates are studied in-depth by the terahertz time-domain spectrum, Fourier transform spectral system, and microwave anechoic chamber measurement system based on a vector network analyzer. The microwave, terahertz, and infrared bands measured the reflectivity of radar-absorbing materials from 1 GHz to 180 THz.The measurement results indicate that as the frequency increases, the surface morphology and roughness of the absorbing material have a certain impact on the reflectivity. Further research has been conducted on the changes in the reflection characteristics of the absorbing material with angles in the terahertz and infrared bands. To further study the absorption principle of the absorbing material in the terahertz and infrared frequency bands, the absorbing layer was peeled off from the metal lining plate and measured. The reflectivity and transmittance of the absorbing coating at 2~180 THz were obtained, and the equivalent dielectric parameters of the composite absorbing material were calculated based on the Kamers-Kronig relation. The test results showed that the absorbing material still has a certain absorption ability in the terahertz and infrared. Infrared is not sufficient to penetrate the reflective coating of the absorbing material to reach the metal lining plate, and its absorption mainly comes from reflection absorption and scattering from the surface of the absorbing material.