Nanocomposites NiCo@C(N)/NC were fabricated by a two-step method, that is, NiCo@C(N) nanocapsules were first prepared by arc-discharge technique, next dopamine (DA) was self-polymerized on NiCo@C(N) surface, which then were subjected to post-heat treatment. The study focuses on the effect of the dopamine content on the microwave absorption performance of the nanocomposites. The acquired nanocomposites NiCo@C(N)/NC were characterized by means of X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and vector network analyzer in terms of their phase composition, microstructure, and electromagnetic properties etc. The results show that the NiCo@C(N)/NC nanocomposites possess excellent wave-absorbing properties when the mass ratio of NiCo@C(N) to DA is 1∶2. Accordingly, the optimal reflection loss is -38.87 dB at a thickness of 3.17 mm and a frequency of 6.61 GHz. It achieves an effective absorption bandwidth of 4.93 GHz when the coating is matched to a thickness of 1.67 mm. The NiCo@C(N)/NC nanocomposites exhibit excellent wave absorbing performance due to the heterogeneous structure of N-doped carbon, defective induced dipole polarization, and the formation of a conductive network, all of which contribute to its high dielectric loss capability. Also, the appropriate amount of N-doped graphitic carbon can effectively improve the electromagnetic synergy effect between the NiCo core and the nitrogen-doped carbon double-shell, thus optimize the impedance matching of the nanocomposites.