The influence of negative refractive index materials on repulsive Casimir forces is studied. The repulsive Casimir interaction is determined by the electric and magnetic properties of the material slabs and the intermediate medium. Through theoretical analysis and numerical calculation, the condition for obtaining repulsive forces is presented. For the negative refractive index materials described by dispersive permittivity and permeability of Drude-Lorentz type, repulsive Casimir force can be realized by tuning the characteristic frequencies.