A type of photonic crystal fiber based on Kagome lattice cladding and slot air holes in a rectangular core is investigated. Full vector finite element method is used to evaluate the modal and propagation properties of the designed fiber. High birefringence of 0.089 and low effective material loss of 0.055 cm(-1) are obtained at 1 THz. The y-polarized fundamental mode of the designed fiber shows a flattened and near-zero dispersion of 0 +/- 0.45 ps center dot THz(-1) center dot cm(-1) within a broad frequency range (0.5 THz-1.5 THz). Our results provide the theory basis for applications of the designed fiber in terahertz polarization maintaining systems.