Metamaterials with subwavelength structural features show unique electromagnetic responses that are unattainable with natural materials. Modulation property is regarded as one of the most important features of metamaterials. At present, the development of such terahertz switches and modulators are relatively slow. So the research of the terahertz metamaterial is very meaningful. The light-control modulation, for example, could control the resonance characteristics of split ring resonators (SRRs) by changing dielectric property of the light layer. Due to the complicated effect in photo-excited layer, we could simplify the research to firstly study the influence of substrate’s refractive index on the resonant behaviors, providing the way to further the investigation of complex problems. In addition, the shape and size of metal microstructure can produce important effect on electromagnetic response. Therefore, based on the finite-difference time-domain method, we have also simulated several SRR structures with different geometry. We find the calculated terahertz transmission spectra exhibit remarkable change, showing that the resonant dips have a red-shift phenomenon and the bandwidth gets narrow with the increased refractive index as well as the structure size. Compared with the geometry effect, the red-shift is more sensitive to the change in refractive index. This work could help us to choose the suitable substrate materials for sample fabrication to realize the specific features.