Three-dimensional Casimir force between two negative-refractive-material slabs is calculated. For the negative-refractive material characterized by dispersive permittivity and permeability of Drude-Lorentz type，the structure of negative refraction frequency band is determined by characteristic frequencies. The different width and depth of the negative refraction frequency bands correspond to reflection properties of different medium，and thus influences the magnitude of Casimir effect between the slabs.