We experimentally investigate the dependences of the surface plasmon polarization (SPP) in the Ag nanowires on the polarizations of the excitation light and the emission light with a wavelength of excitation light 750nm. We find that the excitation and transmission efficiency change obviously with the polarization of incident light. However, the emission light is always linearly polarized light with an unchanged polarization direction. For the nanowires synthesized using a self-seeding process, their ends are axisymmetric. When the direction of the incident light is parallel to these Ag nanowires, the excitation and transmission efficiency of SPP are high. Conversely, when the polarization direction of the incident light is perpendicular to the wire axis, it is very low. For the nanowires with asymmetric ends, when the direction of the incident light has an angle with respect to the Ag nanowires, the excitation and transmission efficiency of SPP are high. While the polarization direction of emission light is always parallel to the wire axis which means that the polarization of the emission light does not depend on the polarization direction of the incident light. The polarization characteristics of the SPP in the thin Ag nanowires can realize the nanoscale manipulation of the intensity and polarization.