Abstract: Three sets of MXene (Ti₃C₂T_x)@nano-Fe₁Co_0.8Ni₁ composites with 15, 45, and 90 mg MXene were prepared by in-situ liquid-phase deposition to effectively investigate the impact of the relationship between MXene (Ti₃C₂T_x) and nano-Fe₁Co_0.8Ni₁ magnetic particles on the electromagnetic absorption properties of the composites. The microstructure, static magnetic properties, and electromagnetic absorption performance of these composites were studied. Results indicate that the MXene@nano-Fe₁Co_0.8Ni₁ composites were primarily composed of face-centered cubic crystal structure particles and MXene, with spherical Fe₁Co_0.8Ni₁ particles uniformly distributed on the surface of the multilayered MXene. The alloy particles had an average particle size of approximately 100 nm and exhibited good dispersion without noticeable particle aggregation. With the increase in MXene content, the specific saturation magnetic and coercivity of the composite initially decreased and then increased, displaying typical soft magnetic properties. Compared with those of the Fe₁Co_0.8Ni₁ magnetic alloy particles alone, MXene addition caused an increasing trend in the real and imaginary parts of the dielectric constant of the composite. Meanwhile, the real and imaginary parts of the magnetic permeability exhibit decreasing trend. With the increase in MXene addition, the material attenuation constant increased and the impedance matching decreased. The minimum reflection loss increased, and the maximum effective absorption bandwidth decreased. When the MXene addition was 90 mg, the composite exhibited a minimum reflection loss of −46.9 dB with a sample thickness of 1.1 mm and a maximum effective absorption bandwidth of 3.60 GHz with a sample thickness of 1.0 mm. The effective absorption bandwidth of the composites and their corresponding thicknesses showed a decreasing trend with the increase in MXene addition, reducing by 50% from 1.5 mm without MXene addition to 1 mm with 90 mg of MXene addition.