Abstract: From double-negative (DNG) metamaterials' constitutive relation, we deduce the differential equations that describe characters of electromagnetic (EM) wave in DNG media. DNG media's three-dimension Finite-Difference Time-Domain (FDTD) formulation is obtained by dispersing those differential eguations. The calculation result is coincident with those in Ref.5. Finally, EM scattering of metallic sphere covered by DNG media or plasma is computed. Because of DNG media's impedance matched to the free space, its absorbing electromagnetic wave character is better than that of plasma.