A broadband terahertz polarization splitter based on filled porous fiber is proposed. The fiber structure is designed by using index converse matching coupling method. The numerical simulation is completed by employing full vector finite element method. The background material is TOPAS. The properties of dispersion and birefringence for before and after filling a common porous fiber are analyzed in detail. It can be found that after interlacing filling to the porous fiber, the mode birefringence of the fiber improves an order of magnitude that changes from 10-3 to 10-2. Then we analyze the properties of terahertz polarization splitter based on filled porous fibers. The numerical simulation shows that the splitting operation can be realized in a broad frequency ranging from 0.8 THz to 2.5 THz. At 1 THz, the splitting length is only 0.77 cm, and the practical material absorption losses for x- and y- polarization are less than 0.20 dB, respectively. The extinction ratios for x- and y- polarization are -12.73 dB and -13.70 dB, respectively. Compared with other designs of dual-core-PCF based polarization splitter, porous fiber is simpler in design, easier in fabrication, and more feasible in experiment. Moreover, this structure has advantages of tunable, low loss and broadband.