A new refractive index fiber optic sensor with low cost, easy operation and the capability of multipoint parallel measurement is explored. A splitter is used in the refractive index fiber optic sensor to achieve multipoint parallel measurement. A high stable amplified spontaneous emission light source and three optical power meters are used as broadband source and detectors, respectively. A simple model is established, and the relation between the ratio of the light power carried by the core versus the total light power of a fiber and the external refractive index (RI) is analyzed in detail. In the experiment, the transmission losses of sample solution with different refractive indices are measured, the calibration curve between transmission loss (TL) and RI by comparison is obtained. It is found that the higher the RI is, the bigger the TL is. The experiment verifies that it can improve the system sensitivity greatly by introducing a fiber Bragg grating.