Abstract: FeSiAl (FSA) alloy, as a typical magnetic wave-absorbing material, demonstrates potential for application in marine equipment stealth and protection. However, its practical engineering use is severely constrained by inherent low-frequency impedance mismatch and high electrochemical activity. To address this, flake-shaped FSA micropowder was modified using air/argon plasma treatment. The surface morphology and compositional changes were characterized via scanning electron microscopy (SEM), X-ray diffractometry (XRD), and X-ray photoelectron spectroscopy (XPS). Combined with electrochemical tests and vector network analyzer (VNA) measurements, the synergistic regulation mechanism between corrosion behavior and low-frequency electromagnetic wave loss performance was systematically investigated. The results show that plasma treatment under different atmospheres did not significantly alter the composition of FSA but primarily affected its surface microstructure. FSA-Air exhibited a rich fibrous structure on its surface, while FSA-Ar mainly showed a granular structure. At a thickness of 5 mm, FSA-Air achieved an EAB of 0.36 GHz (0.59–0.95 GHz) and a RLmin of -16.65 dB, significantly outperforming untreated FSA. Additionally, the corrosion resistance of FSA-Air was notably improved, with the corrosion current density decreasing from 7.25×10-6 A·cm-2 to 1.85×10-6 A·cm-2.