According to terahertz time domain spectroscopy, terahertz (THz) transmission characteristics of metal sub-wavelength slit array structure are researched. The results show that surface plasma wave resonance of metal slit array structure can be excited by THz wave, the super-strong transmission phenomena in THz transmis. sion waveband is produced by the resonance. For surface plasma resonance effect, very high degree of polariza. tion of transmission THz will be produced by the slit structure. The experimental results as benefit references are provided to the production of THz polarization devices.