Environmentally-friendly magnetic metallic absorbers with high-performing antioxidant property, thermal stability, and anti-corrosion capability have attracted great attention in real-world applications. A surface modification technology of magnetic metallic absorbers with dense and inert materials has been an effective strategy to solve the aforesaid problem. Herein, fluorine-free core–shell carbonyl iron-organic silicon absorbers (CI@SiO₂/1,1,1,3,3,3-hexamethyl disilazane (HMDS)) were fabricated via a facile one-pot synthesis using tetraethyl orthosilicate (TEOS) and HMDS as the precursor of protective layer (SiO₂/HMDS), and CI@SiO₂/HMDS hybrid reveals its long-term corrosion resistance and excellent microwave absorption performance with a minimum reflection loss value of −44.3 dB and an effective absorption bandwidth of 5.3 GHz at a thin thickness of 2.0 mm after immersion in 5.0 wt.% NaCl acidic solutions for 2,160 h. Meanwhile, CI@SiO₂/HMDS hybrid can still achieve the maximum radar cross-sectional (RCS) reduction values about 16.5 dB·m² at the detection θ of 0°. The exceptional microwave absorption performance and structural stability are largely due to the extraordinary wave-transparent property and shielding ability against corrosive medium of SiO₂/HMDS hydrophobic protective layer with a contact angle of 132.5°. The research paves the way for the large-scale and batch production of high-performance magnetic metallic absorbers and increases their survivability and reliability in the harsh environments.