The effect of refractive index on extraordinary transmission properties for metal-dielectric-metal photonic crystal (M-D-MPhC) by changing a thin dielectric layer is studied. Three M-D-MPhC structures combined with square lattice round holes array with different refractive indexes [nd（SU-8）=1.6, nd（SiO2.1N0.3）=1.6 and nd（SiO0.6N1)=1.8] are fabricated using compatible technology with CMOS process, and their transmission spectra are measured using Fourier transform infrared spectrometer. It is found that Au-SiO2.1N0.3-Au structure can obtain better effect of light transmission enhancement and narrower transmission peak in experimental results. It is demonstrated that extraordinary transmission properties for M-D-MPhC depend strongly on both the size of refractive index of middle dielectric and its material fabrication process difference. The finite-difference time-domain (FDTD) method is used to simulate transmission spectra and electric field intensity density distribution of M-D-MPhC with refractive index of 1.6 and 1.8 respectively under the same conditions. Simulation results agree well with the experimental findings.