Based on the finite-difference time-domain (FDTD) method, the terahertz (THz) polarization characteristics of a metal wire grid structure are simulated and analyzed. The influences of duty ratio and metal layer thickness on the polarization characteristics are investigated. It is found that the periodic high transmission phenomenon in the range of 0.1-10 THz occurs with the increase of the metal layer thickness. The metal wire grid THz polarizer is fabricated by the femtosecond laser micro-machining technique, which is tested by the time-domain terahertz spectroscopy system. The experimental results are consistent with the simulation ones. The extinction ratio of the polarizer is in the range of 40 dB-45 dB and the polarization degree is 1, which indicates that the polarizer possesses a good polarization characteristic.