Ground penetrating radar (GPR) has been widely used for non-destructive evaluation (NDE) of concrete structures, which are usually reinforced by steel rebar. This paper investigates the penetration and scattering of electromagnetic waves through rebar nets. A numerical model simulating an infinite rebar net is established, as shown in Figure 1(a). To save the computation resource and time, only two rebar, respectively in the x and y directions, are modeled. A perfect electric conductor (PEC) condition and a perfect magnetic conductor (PMC) condition are applied to the two boundaries. Consequently, an infinite periodically-spaced rebar net is modelled, according to the mirror’s principle. In this model, two layers of rebar net with an air spacing in the z direction are included.