In terahertz frequencies, using refractive index matching coupling principle, a broadband polarization splitter based on orthogonal hollow core was designed. Compared with the traditional separation device, it has the following advantages: (1) the refractive index matching degree of dual-core is high, making the separation length of the corresponding polarization mode is very short; (2) the dual-core are filled with air, which can reduce the absorption loss to THz wave; (3) through the design, making the dual-core perpendicular, thus the refractive index curve of y polarization mode overlap with that of x polarization mode, greatly expanded the scope of bandwidth. Its working bandwidth reached 0.17 THz. In addition, because of its structure is simple and symmetry, the THz fiber is easy to fabricate, which has a high application value in the terahertz network.