The construction of 3D porous structures and metamaterials (MMs) is the most promising approaches to achieve broadband electromagnetic wave (EMW) absorption. However, it is still a huge challenge to achieve multispectral ultra-broadband EMW absorption properties compatible with low-frequency band (L- and S-band) due to its ultralong wavelength and strong bypass capability. Herein, magnetic–dielectric synergistic gradient MMs (MDSGM) consisting of oriented flaky carbonyl iron (FCI) film and periodical RGO/CNT/CNF aerogel (GTFA) array are demonstrated. Benefiting from the synergistic effect of strong magnetic–dielectric loss, structural loss, and excellent impedance matching, MDSGM harvests an exciting multispectral ultra-broadband EMW absorption performance with a remarkable effective absorption bandwidth covering the whole measured frequency of 1–40, 50–110 GHz, and 0.1–2.0 THz for the first time. The minimum RL (RLmin) reaches −40.24 dB and average RL is up to −19.3 dB (98.8% EMW being absorbed) in microwave band. Moreover, this multispectral ultra-broadband EMW absorption property is less affected by the incident angle. This work pioneered realization of multispectral ultra-broadband EMW absorption compatible with low-frequency, which provides a great thrust for the development of stealth technology in the upcoming smart era.