Achieving compatible electromagnetic (EM) defense across both microwave and Terahertz (THz) regimes remains a formidable challenge in the development of advanced stealth materials. Herein, a novel MXene/liquid metal (LM)/Ni chain composite is strategically engineered through an interfacial synergy modulation and one-dimensional (1D) magnetic structure induction strategy, enabling high-efficiency co-attenuation across the microwave-THz spectrum. This architecture synergistically combines the conductive network of MXene, LM-induced interfacial polarization, and the magnetic loss from Ni chains to achieve superior impedance matching. Remarkably, with a mere 5 wt.% filler loading, the composite achieves a record-low reflection loss (RL_min) of −63.1 dB and an effective absorption bandwidth (EAB) of 6.72 GHz. Simulation results further validate its immense potential for radar stealth applications in both civil and military coatings. When fabricated into flexible films, the material demonstrates exceptional EM attenuation in the 0.1–1.6 THz band, yielding a shielding effectiveness (SE) and absorption efficiency of 69.6 and 68.1dB, respectively. Mechanism analysis reveals that the multiscale conductive network, pronounced interfacial polarization, and magneto-dielectric synergistic loss collaboratively facilitate high-efficiency energy dissipation across multiple frequency bands. This work provides a novel design strategy for the development of lightweight, ultra-thin, and ultra-broadband microwave-THz absorption/shielding materials.