Due to the increasing demand for dynamically reconfigurable properties in building intelligent optical interconnects, a reconfigurable polarization beam splitter (PBS) on a lithium-niobate-on-insulator (LNOI) platform using a triple-waveguide coupler was implemented. The output port of the transverse magnetic (TM) mode can be controlled by adjusting the phase state of the optical phase change material (PCM) to realize the reconfigurable function. A 3D finite difference time domain (3D-FDTD) method was also employed to investigate the performance and to optimize the structure of the PBS. The results show that the TM and transverse electric (TE) modes can be efficiently separated when PCM is in the amorphous state, where the extinction ratio exceeds 20 dB in the wavelength range of 1530?1580 nm under the TM mode and an ultra-low insertion loss is incurred under the TE mode (approximately 0.03 dB). When the PCM switches into the crystalline state, the TM and TE modes transmit along the input waveguide, and the reconfigurable function is enabled, where the size is 35 μm, which is compact for integration. Finally, the fabrication tolerance of the device is investigated, and the results indicate a certain degree of robustness.