In this study, porous carbon nanoflowers (PCF) are synthesized using MIL-101-NH₂ as the precursor, and niobium single atoms (Nb-SAs) are anchored on the PCF via ion adsorption and high-temperature pyrolysis processes (Nb-SA/PCF). Structural characterization and density functional theory (DFT) calculations demonstrate an asymmetric coordination environment of Nb-SA, with three in-plane nitrogen atoms from the graphene and two axially oriented oxygen atoms coordinating each niobium center (NbN₃O₂). This asymmetric NbN₃O₂ enhances charge transfer and increases the dipole moment, thereby significantly improving polarization loss. Consequently, the Nb-SA/PCF-based film exhibits an effective absorption bandwidth of 6.00 GHz at a thickness of 2.0 mm. Moreover, the film demonstrates outstanding mechanical strength, flexibility, thermal insulation, and hydrophobicity, broadening its potential for operational applications in demanding environments.