The invention discloses an ultra-wideband wave-absorbing structure for reducing the RCS of an antenna. The ultra-wideband wave-absorbing structure comprises a surface skin dielectric layer, an impedance matching dielectric layer, an impedance type frequency selective surface, an impedance type frequency selective surface substrate, a dielectric layer and a conductive reflecting layer which are arranged from top to bottom, the impedance type frequency selective surface is composed of N * N conductive units, each conductive unit comprises a conductive outer circular ring and a conductive inner circular ring which are concentrically arranged, and each conductive circular ring is uniformly loaded with four resistors. According to the ultra-wideband wave-absorbing structure for reducing the RCS of the antenna, the resistance loading double circular rings are adopted as the impedance type frequency selective surface, so that the RCS of the antenna can be reduced, the purpose of hiding the antenna is achieved, and the ultra-wideband wave-absorbing structure is stable in performance and has a wide practical application prospect.