Abstract: A numerical method for calculating the reflection coefficient of the impregnated absorbent honeycomb with plane wave normal incident to its broad face is presented. By introducing a concept of impedance for the honeycomb wall and by the assistance of the periodic Green's function, the Electric Field Integral Equation for the infinite honeycomb surface is established and the unknown surface current is solved by the method of moment. Numerical results are obtained for various heights, different absorbent parameters and various impregnated thickness within the frequency band 8~12 GHz. It shows the proposed method is of high efficiency and can be used in the honeycomb fabrication and application of structural absorbers.