A plasmon Fabry-Pérot (F-P)cavity，composed of the silver nanowire pairs and gold film，is prepared using the bottom-up nanofabrication process． Combing the dark-field scattering spectroscopy and numerical simulation，it is revealed that the surface plasmon polariton propagating on the metal surface is multi-reflected by the nanowires，rendering a standing wave in the cavity and a multi-beam interference modulated spectral line-shape．Furthermore，the refractive indices of glycerol solutions with different concentrations are measured using the F-P cavity，suggesting a linear redshift law of the cavity resonant wavelength with increasing of the refractive index of the solution．Finally，by tuning the length of the F-P cavity，the highest detection sensitivity of 555 nm/ＲIU is derived．