Abstract: In order to meet the demand of structural absorbing materials for thermal vacuum absorbing box used in the satellite communication system examination, a lightweight pyrolytic carbon-based foam structural absorbing material was prepared by precursor method and pyrolysis process in this article. The performance test results show that the material is not only suitable for high vacuum, high and low temperature cycling in thermal vacuum absorbing box, but also is with electromagnetic characteristics in wide frequency band, wide temperature range, and high dielectric loss, which is suitable for the design of high efficient sharp cone absorbing structure. On the basis of this work, taking the development of a passive intermodulation (PIM) absorbing box as an example, simulation models of electromagnetic wave far-field plane wave irradiation at room temperature and electromagnetic wave near-field spherical wave irradiation at wide temperature range were established respectively. Based on the simulations of the two models, specific dimensions of sharp cone + bottom plate structure of the absorbing material were determined. The results indicate that its absorbing performance meets the assessment requirements of the national military standard of China.