We present experimental and numerical studies on the enhanced light narrow transmission through cascaded Au/SiOxNy/Au aperture arrays by varying the refractive index and thickness of SiOxNy.It is found that the enhancement as well as narrowing of the optical transmission originates from the coupling role of surface plasmon polaritons.The results indicate that the transmission enhancement is highly dependent on the refractive index and thickness of SiOxNy.A higher transmission efficiency and narrower peak are obtained in Au/SiO2.1N0.3/Au structure with a small refractive index (1.6) and thin thickness (0.2μm).