A broadband terahertz (THz) polarization beam splitter (PBS) was proposed. The PBS was based on subwavelength grating sandwiched between silica layers, which could split an arbitrarily polarized optical beam into two orthogonal, linearly polarized components, and then reflected the TE mode and transmit the TM mode. It was shown that THz PBS could efficiently operate from 3.5 THz to 5.5 THz, with high diffraction efficiencies and extinction ratios. In the process of PBS manufacture, there would be unavoidable deviations of the geometric parameters, which may affect its properties, i.e. the diffraction efficiencies and extinction ratios. Therefore, some structure parameters were calculated. Those values suggested that the designed PBS allows sufficient manufacture tolerances. When D1 ranged from 1 μm to 1.2 μm and thickness D3 ranged from 2.8 μm to 3 μm, the values of TTM0 are always more than 96.9% and those of R0TE are more than 98.7%. And the values of Tc and Rc were respectively kept higher than 31 dB and 33.4 dB. These results show the PBS with a frequency bandwidth of 2 THz, a large angle range of 10°, an extinction ratios over 20 dB and a diffraction efficiencies over 90%, is obtained. This work may inspire related studies and achieve some potential applications in THz manipulation system.