Abstract: The absorbing properties of single-layer and bi-layer structural carbon black/ABS microwave absorbing material within the frequency range of 8-12 GHz were studied.The absorbing properties of bi-layer structure were obviously improved,compared with those of single-layer one.The design parameters of bi-layer had different degrees of effects on absorbing properties.When the parameters of absorbing layer were fixed,the properties of bi-layer structural carbon black/ABS material,with 5% carbon black as transforming layer were relatively good.When the parameters of transforming layer were fixed,the properties of bi-layer structural material were obviously improved if the carbon black content was 30% or the thickness of absorbing layer was 6 mm.The optimum combination of bi-layer structure microwave absorbing material was 3 mm thick transforming layer with 5% carbon black and 6 mm thick absorbing layer with 30% carbon black.