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In this study, an all-dielectric metasurface is proposed, whose unit cell is composed of a silicon elliptical disk and a silicon elliptical ring. The transmission of the structure were analyzed by using three-dimensional finite-difference time-domain method. In the wavelength range of 800 to 1200 nm, four sharp Fano resonances appeared in the transmission spectrum. The maximum quality factor reached 7421. Furthermore, we analyzed the electromagnetic field distributions corresponding to the four peaks, and evaluated the contributions of multipoles in forming the resonant responses. Besides, we investigated the influence of different structural parameters, including the length of the semi-major axis, the height of the elliptical disk and ring, and the period length, on the four resonance peaks. Finally, based on the high quality factor, we studied the refractive index sensing characteristics of the structure. By optimizing the structural parameters, the sensitivity and the figure of merit could reach up to 392 nm/RIU and 3001, respectively. Therefore, we believe that the proposed structure exhibits broad application prospects in refractive index sensors.