A compact polarization beam splitter (PBS) based on a silicon waveguide-silver nanoribbon-silicon waveguide is proposed and demonstrated numerically by utilizing the evanescent coupling between a strip-nanowire and a nanoslot waveguide. Two-dimensional (2-D) FDTD simulations were performed to elucidate the properties of surface plasmon polaritons (SPPs) in this device made from silicon-metal-silicon, and were found to agree well with the theoretical predictions. TE and TM polarized light are respectively separated into two different output ports of Y-shaped silicon waveguide in which the coupling efficiency is 62% and 45% for 1.55μm wavelength, respectively. The proposed PBS structure could be utilized to develop ultracompact optical polarization modulating device for large-scale photonic integration and optical information processing.