The structure of the parallel metallic slabs with middle-part-indentation is based on the parallel metallic wires. The permittivity of the structure is negative in a certain frequency range because of the effect of the plasma. And the strong magnetic resonance occurs in the special frequency range because the middle-part-indentation is introduced in the parallel metallic slabs. The result of simulation shows that the structure composed of ceramic alumina has negative permittivity and permeability in the X-band. The range of the double negative （εμ<0） varies with the resonance frequency. Theoretical analysis, which is in agreement with the results of simulation, indicates that the resonance frequency is related with the width of metallic slaps, height of indentation and the width of the middle-part of the structure.