A novel and compact terahertz (THz) polarization beam splitter based on photonic crystal is proposed. Transmission without diffraction of transverse electric (TE) and transverse magnetic (TM) modes is realized by using the self-collimating effect, while the separation of TE and TM modes is realized by using the band gap characteristic. The characteristics of the terahertz polarization beam splitter is simulated and analyzed by using plane wave expansion method and time domain finite difference method. The results show that the polarization beam splitter can realize polarization separation in the frequency range of 2.9-3.01 THz. While the frequency is 3 THz, the reflectivity of TE mode and the transmittance of TM mode are both higher than 90%. The extinction ratios of TE and TM modes are 19.9 dB and 26.24 dB, respectively. Moreover, compared with the previous photonic crystal terahertz polarization beam splitters, the proposed polarization beam splitter is simpler to design, easier to realize (without defects), smaller in size (650 μm×650 μm) and wider in bandwidth (2.9-3.01 THz).