With the accelerating development of electronic technology, how to effectively eliminate electromagnetic radiation pollution has become a critical issue. Electromagnetic wave (EMW) absorption materials have an irreplaceable position in the field of military stealth as well as in the field of electromagnetic pollution control. In order to cope with the complicated electromagnetic environment, the design of multifunctional and multiband high-efficiency EMW absorbers remains a daunting challenge. In this work, a hierarchical porous molybdenum carbide matrix with a three-dimensional porous structure was designed by salt melt synthesis (SMS) strategy. Furthermore, the relationship between the structure and the impedance matching performance was explored by stepwise modification via ultrathin layered MoS₂ nanoflakes. Analysis indicates that the extent of modification of hierarchical porous molybdenum carbide by MoS₂ nanoflakes modulates the dielectric performance due to differences in morphology and the introduction of heterogeneous structures, along with a dramatic impact on the impedance matching performance. In particular, the prepared MS/MC/PNC-2 composite exhibits a reflection loss (RL) of −55.30 dB at 2.4 mm, and an ultra-broad effective absorption bandwidth (EAB) of 7.60 GHz is obtained at 2.0 mm. The coordination of structure and component enables the absorber to exhibit strong absorption, wide bandwidth, thin thickness, and multi-band absorption characteristics. Noticeably, the effective absorption performance in the broadband for X and Ku is also satisfying, as well as possessing moderate marine anti-corrosion performance. This study contributes to an in-depth understanding of the relationship between impedance matching and EMW absorber performance and provides a reference for the design of multifunctional, multiband microwave absorbing materials.