A model of refractive index sensing with high sensitivity elliptic side core surface plasmon resonance (SPR) based on dual-core photonic crystal fiber (PCF) is proposed. Properties of a sensor are analyzed by the full vector finite element method with the boundary condition of anisotropic perfectly matched layer. Results show that SPR can be realized in elliptic side core coated with silver nano-layer, and the resonance peak is highly sensitive to the changing refractive index of inspection hole. Compared with that of the circular structure, the phase matching between the fundamental mode of fiber core and the metal surface plasmon polariton (SPP) mode of the elliptic side core structure is easier to implement. When the ellipticity is 0.7, a sensitivity of 10412 nm·RIU-1 in a refractive index range from 1.45 to 1.50 can be obtained, and the sensing curve has high linearity. In addition, the elliptic side core structure can effectively restrain the high-order SPP mode. The interference introduced by the coupling between fundamental mode and many SPP modes can be avoided.