In this paper, a two-core terahertz fiber directional coupler is proposed. Two dielectric cylinders are suspended in the interior of two annular dielectric layers to form two fiber cores. By adjusting the structural parameters, the coupling length of the two polarization modes can be equal, thus realizing polarization independence of the coupling length. The length of the coupler can be one half of the coupling length of the fiber mode, and the transmission loss can be reduced with the short length of the device. The coupler is numerically analyzed by finite element method. The results show that the length of the coupler is 0.535 cm, and the transmission loss of x and y polarization modes is 0.23 dB and 0.19 dB, respectively. Under the premise that the coupling length difference between the two polarization modes is less than 1%, the bandwidth reaches 220 GHz.