Orbital angular momentum (OAM) waveguides are critical for multi-channel photonic-on-chip applications. However, current large-mode-area waveguides pose a challenge for OAM device miniaturization. Here, a novel hybrid plasmonic waveguide is theoretically proposed to decrease the OAM mode area by two orders of magnitude. Benefiting from the Ag-As₂S₃-SiO₂-As₂S₃-Ag five-layer cylindrical structure, the guided OAM mode realizes a larger figure of merit of 88. Based on this waveguide, an OAM coupler with a record-breaking small footprint (0.68 µm × 5.7 µm) is designed. The proposed waveguide enables subwavelength OAM light transmission, which provides a key building block for high-density OAM photonics circuits.