Abstract: The surface of flaky metal magnetic powders with diameter size of 5 μ m and thickness of 1 μ m was modified by SiO₂. The appearance, structure and phase constitution of the powders before and after treatment were characterized by SEM, TEM and RA-IR. And the powders were randomly dispersed in paraffin at a mass ratio of 5 ∶ 1 for microwave electromagnetic parameters test and comparison in the frequency range of 2~18GHz. The results show that a high resistivity film is formed on the powder surface, and the real and imaginary parts of complex permittivity of the sample decrease by 20 and 7 in average but the corresponding complex permeability decreases slightly. The coatings with thickness of 1mm give a microwave absorption of 8dB with a band width of 7GHz (7.6~14.6GHz) and the microwave absorption of the modified flaky metal magnetic powders is improved.