Plasmonic waveguides have been indispensable "building-blocks" to construct functional elements for future integrated nano-photonic devices and circuits. In this paper, we demonstrate that a thick silver nanowire with well-defined end facets can provide multiple outcoupling channels, and the controllable beam splitting is realized. The propagating surface plasmons emission at nanowire end are split into two parts: I1 and I2, with the polarizations nearly perpendicular to the respective emitting facets. By changing incident polarization, the splitting ratio (I1/I2) can be tuned in the range of 1.52~0.36. Electromagnetic simulations indicate that polarization beam splitting mechanisms in this single thick nanowire are the interference of propagating surface plasmon modes and the superposition of excited dipoles at the nanowire end. These findings would deepen the understanding of manipulation of surface plasmons propagation/emission, and advance the development of plasmonic waveguide-based nano-photonic devices.