We numerically study the negative index properties of sandwiched metamaterials,perforated with a square array of circle holes filled with different media.Transmission spectra indicate that the filling medium can effectively change the position of the localized resonant peak,while keeping the position of the other transmission peaks hardly changed.Reflection spectra and retrieved effective impedance verify that an appropriate choice of the filling medium can provide a perfect impedance match.Due to the perfect impedance match,the electromagnetic responses of the negative index band based on the inteal surface plasmon polaritons change in many aspects,such as a stronger magnetic resonance,a higher figure of merit and a narrower negative refractive index band.