Terahertz (THz) spectroscopy is becoming crucial in analytic chemistry to complement molecular properties of infrared ray spectroscopy. Following the basis of THz spectroscopy, THz-sensing technique plays an important role to develop the applications in THz region. THz-waveguide sensors are sensitive to molecules with minute amounts, like the particles and droplets. Due to the microstructure, photonic crystal (PC) THz waveguides are agreed as one excellent optical sensor. One- and two-dimensional PC waveguides have been presented [1, 2], but the sensing application does not work well. This is because the micro-structure space is enclosed by the metal substrate without open space to load analytes. It is also a serious issue to use the dielectric PC fiber even though the nano-liter of liquid analytes can be recognized in theory. In the presentation, an open frame of PC chip is demonstrated in a metal rod array (MRA) structure. There are photonic band gaps to forbid THz photon’s delivery and demonstrated in prior works . The air gap size in a structural pitch modifies not only the photonic band gaps but also the waveguide modal confinement. Based on the investigation results in the presentation, the gap size should reduce to strictly confine THz field with strongly oscillation inside the MRA medium. A 420 m-period MRA is demonstrated to deliver THz waves of 0.40 ~ 0.65 THz with well confinement, where the electric-field strictly oscillates among the rods along the optic axis.