FSA powder is of crucial importance to microwave absorption material because of the higher magnetic permeability and saturation magnetization. However, poor resistance to salt spray corrosion limits its further application in extreme environment (marine and damp heat, etc.). Therefore, SiO2 and carbon layers are in situ deposited on FSA surface by using the St?ber process and catalytic chemical vapor deposition technology to form FSA@SiO2@C composite structure. Furthermore, the anti-corrosion electromagnetic properties of the composite mechanism are studied by network vector analyzer and electrochemical test. The SiO2 and carbon layers are uniformly coated on the surface of the FSA and tightly combined with it. The thickness of the SiO2 is about 100 nm, and the thickness of the carbon is about 5 nm. The SiO2@C reduces the corrosion rate of FSA from 2.66×10-12 to 1.52×10-12 m/s, which significantly improves the corrosion resistance of FSA in salt spray environment. When the matching thickness is 3 mm, the microwave absorption properties of FSA@SiO2@C is significantly improved compared with FSA. The absorption bandwidth is expanded from 4.2 GHz to 5.84 GHz, and the RLmin reach as low as -21.65dB (7.41GHz), which is less than -19.03 dB (5.93 GHz). of pure FSA. The multi-shell composite structure can significantly improve the corrosion resistance and microwave absorption performance of FSA, and provides a feasible design idea for the multi-functional magnetic metal microwave absorbing materials with anti-corrosion and high efficiency.