A novel ultra-wideband polarization beam splitter (PBS) with dual-core conjoined tube negative curvature fiber (DC-CTNCF) is studied and proposed. By introducing a double conjoined tube in the x-direction, the extra loss caused by inter-tube coupling and vibration can be reduced, and the crosstalk effect between adjacent tubes can be suppressed, which in turn improves the performance and stability of the DC-CTNCF PBS. By optimizing the fiber structural parameters, the DC-CTNCF PBS with a length of only 5.03 mm achieves an ultra-wide bandwidth of 590 nm in the wavelength range of 1.44 to 1.99 μm, and the ratio of the loss of the higher-order modes (HOM) to the fundamental mode is larger than 100 in the corresponding wavelength range, indicating that the PBS has excellent single-mode properties. The DC-CTNCF PBS represents a significant improvement in the fields of fiber optic communications and fiber optic sensing, as it surpasses the length limitation of current PBS designs and increases the coupling length by an order of magnitude.