We study the mechanism of microwave response properties of SiCp/paraffin nanocomposites and propose a mi-crowave absorption model of nanocomposites based on the conservation law of energy and the theory of electro-magnetic scattering. Using the model we calculate the reflectivity of SiCp/paraffin nanocomposites ranging from 2 CHz to 18 GHz. The calculated results are very consistent with the experimental data in the frequency range investigated.