A compact tunable quintuple Fano-like plasmonics structure, composed of a metal-insulator-metal, a baffle, a quarter ring and a rectangular cavity, was proposed and applied to refractive index sensor in this paper. According to the numerical simulations, quintuple Fano resonances, which derived from the coupling and interference between the narrow discrete state supported by the quarter ring and the rectangular cavity and the broad continuum state excited by the baffle, were obtained in its transmission spectrum. Additionally, the quintuple Fano resonances obtained can be easily tuned by changing the geometric parameters of the resonators. Because of the sharp asymmetry of Fano resonance, the proposed system can be served as a high efficient refractive index sensor with a sensitivity of 1600 nm/RIU and figure of merit (FOM) of 6743. Considering the development of high integrated photonic circuits, it is believed that the proposed structure can find significant applications in optical sensing and optical communication areas.