0D-2D Polydopamine (PDA)-derived carbon nanoparticles @ MXene composites (PCM) with high microwave absorption properties were prepared by in-situ self-polymerization combined with vacuum pyrolysis. As the “nano clothing” of MXene, the moderate accumulation of PDA-derived carbon nanoparticles makes enough interface contact with MXene nanosheets, which not only improves the impedance matching of MXene reasonably but also optimizes the dielectric loss. Based on the multi-dimension structure and multi-component synergistic effect, when the filling amount of the composite is only 7.5 wt% and the thickness is 2.8 mm, the best reflection loss at 10 GHz is −46.92 dB and the maximum effective absorption bandwidth is 7.01 GHz. This work provides a synthesis strategy of crystal/amorphous heterointerface and offers a new way for the preparation of lightweight, broadband, and efficient microwave absorption materials, showing great application potential.