Based on strong interference theory and the assumption of long wave band，formulae for computing the equivalent electromagnetic parameters of honeycomb-structured absorbing materials are presented. It is pointed out that the equivalent permeability and permittivity of honeycomb-structured absorbing materials are smaller than those of the absorbing layer， but the equivalent permittivity is reduced more significantly， so the equivalent permeability is more close to the equivalent permittivity. This is helpful for the design of impedance matching of absorbing materials. It is indicated by reflectivity results that the absorbing layer should have an optimum thickness to make the reflectivity minimal for honeycomb-structured absorbing materials with different height of honeycombs. These results are useful for design of honeycomb-structured absorbing materials.