A metal nano-gap array with polarization-dependent optical properties prepared by self-assembly technology of microspheres is proposed. The structure is fabricated based on the mask of periodic polystyrene (PS) microsphere film, followed with tilted vacuum evaporation coating of metal film. The relationship between the transmission spectrum of the nano-gap array and the incident polarization angle is measured, and it exhibits polarization-dependent properties that can be used as optical switches. The finite-difference-time-domain (FDTD) method is used to simulate the transmission spectrum of the nano-gap array and the electric field intensity distributions at the resonant wavelengths. Furthermore, the surface plasmon modes and the influence of geometry parameters on transmission spectra are studied. The refractive index sensitivity of this structure reaches as high as 992 nm/RIU.