By launching surface plasmons propagating along the Ag nanowire deposited on a substrate,we clearly observe three leaky modes using the Fourier imaging method.The effective refractive indexes,propagation lengths and electric field distributions of the modes are investigated,which indicate that the energy of the mode with a lowest effective refractive index is mainly distributed in the air,while for the other two modes,it is mainly distributed in the substrate and in the gap between the Ag nanowire and the substrate.These modes enable such a configuration to be used as a multichannel waveguide or highly directional optical antenna,which is of fundamental importance for optical device miniaturizations and photonic circuit integrations.