A novel and compact distributed refractive index (RI) sensor based on Rayleigh backscattering and macrobending single mode fiber (SMF) is proposed and experimentally investigated. Our proposed sensor is simply fabricated by bending a piece of SMF to a radius of curvature in several millimeters. We detect the refractive index of the external medium surrounding the macrobending fiber, for the first time, by analyzing the Rayleigh backscattering signals recorded from optical frequency domain reflectometry. We measure the range of the RI from 1.3348 to 1.3557 using the proposed method. To verify the capability of the distributed sensing, we also use this sensor to detect multipoint RIs simultaneously. The RI measurement sensitivities are 2319.24 GHz/RIU (18.55 nm/RIU) and 2717.85 GHz/RIU (21.74 nm/RIU) with bending diameters of 12.2 mm and 11.3 mm, respectively. In addition, our macrobending fiber has its original buffer coating remaining intact, allowing the fiber to maintain optimal mechanical property and be suitable for more practical applications.