In this thesis, we designed the semi-coaxial metal hole arrays with a different lattice constant, period, film thickness, and the arrangement of two metallic sectorial holes to study the influence of these different geometrical parameters on the extraordinary optical transmission phenomenon. We measured these samples by terahertz time-domain spectroscopy (THz-TDS), and discussed the physical picture by using finite difference time domain (FDTD) method. When we varied the lattice constant and period of semi-coaxial metal hole arrays, the extraordinary optical transmission is observed in those samples with the surface plasmon frequencies higher or close to the cut-off frequency of metallic sectorial waveguide, and the electric field is distributed in the metallic hole. For the samples with the surface plasmon frequencies lower than the cut-off frequency of metallic sectorial waveguide, the transmission peaks are decayed rapidly as the period of hole arrays is increasing. As we varied the thickness of a metallic film, we found the transmission peaks decayed as the film thickness is increased, but the peak frequencies are unchanged. In the experiment of the variation of the arrangement of two metallic sectorial holes in a unit cell, we observed the peak frequency shifted to the lower frequency when the distance between two metallic sectorial holes of one unit cell shifted from 40um to 300um in the horizontal direction. Also in the vertical direction, the distance between two metallic sectorial holes of one unit cell shifted from 0um to 300um, we found the peak frequency shifted to the lower frequency.