Abstract: Epoxy resin based double-layer composite coatings (matching layer and absorbing layer) with impedance gradient structure were prepared with thickness of 1.2 mm, employing carbonyl iron (CI) and carbon black (CB) as absorbents in the matching layer and absorption layer respectively, in which SiO₂ was introduced into the matching layer as wave-transmission material to improve the matching impendence. With increasing SiO₂ content in the matching layer, the reflection loss (RL) was enhanced in the frequency range 2 ~ 18 GHz. The optimized SiO₂, CI and resin weight ratio (SiO₂: CI: ER) was 2:5:1, when the optimal RL got to- 17.3 dB and the effective absorption band (RL <- 4 dB) reached 5.7 GHz.