A rGO/Nb2CTx/Fe3O4 composite with a hierarchical architecture is prepared by integrating multilayered Nb2CTx, magnetic Fe3O4 nanoparticles and two-dimensional rGO sheets. The rGO/Nb2CTx/Fe3O4 composite shows superior absorption of electromagnetic wave with a minimum reflection loss (RLmin) of −59.17 dB at 11.8 GHz with an equal absorber thickness of 2.5 mm as well as a broad effective absorption bandwidth (EAB, RL ≤ 10 dB) of 6.8 GHz. The tunable EAB can be achieved at a frequency range of 8.5 to 18 GHz by modifying the thickness of the absorber from 1.5 to 3 mm. The excellent absorption capacity of electromagnetic wave is attributed to the synergetic effects between the multiple loss mechanisms of rGO/Nb2CTx/Fe3O4 and good impedance matching. The results provide new insight into MXene-based absorbers with enhanced ability to absorb electromagnetic wave by incorporating the magnetic components and 2D rGO sheets.