A novel dual-core structure based on cyclic olefin copolymer (COC) photonic crystal fiber (PCF) is proposed for realizing Terahertz (THz) polarization beam splitting. The dependence of coupling length and structural parameters of the THz polarization beam splitter (TPBS) is analyzed. The confinement loss, effective material loss, and extinction ratio (ER) are examined. The numerical simulation results show, two orthogonal polarization modes are separated completely within a device length of only 45.16 mm owing to the different coupling length in x- and y-polarization directions. The maximum polarization ER of 107.7 dB is obtained at 0.54 THz. The bandwidth with ER greater than 20 dB reaches 0.02 THz. The proposed compact dual-core TPBS will find extensive applications in THz photonic systems. © 2022 Wiley Periodicals LLC.