A kind of novel fiber, comprising two fiber cores which are suspended in air inside the outer cladding via a central thin membrane, is proposed for optical switching application. When a hydrostatic pressure applied on the optical fiber, the pressure-induced refractive index change of the two fiber cores will contribute to the periodical change of the intensity of guided light in the fiber core. The mode coupling of two cores under different hydrostatic pressure and influences of each structure parameter of the proposed fiber on the switching pressure have been numerically investigated.