Based on the equivalent circuit model theory, a rectangular metal ring with two interlaced multi-openings is placed on one side of the dielectric substrate, and thus a new kind of material structure is formed. Its effective electromagnetic parameters are extracted via the theoretical analysis and simulation. The results show that, the effective permittivity and effective permeability of this structure are both negative in the spectral range of 40.8-61.8 GHz, the absolute bandwidth is up to 21 GHz, and the wideband characteristic is achieved. These results provide an important reference for the application of left-handed materials in millimeter wave communication.