In the experiments of THz wave transmitting through the metallic cylindrical gratings fabricated by sub-wavelengthbrass wires, this paper reports that the discrepancy in the sharp resonances occurred as the grating perpendicular orparallel to the electric vector are observed. A simulation based on the finite difference time domain (FDTD) indicatedthat the enhanced transmission through the grating is attributed to the combined effects of surface plasmons andcavity modes in the perpendicular condition, while the cavity modes dominate the resonant transmission under theother conditions. Additional experimental data and calculated results show that ～1 enhanced coupling efficiency canbe realized in some THz frequency, which could be applied to the design and improvement of various optoelectronicdevices, or detection of biological molecule and powder samples, etc.