A temperature and refractive index dual-parameter sensor composed of a cascade of a single-mode fiber Bragg grating and a multi-mode Fabry-Perot cavity is proposed. The end of the multi-mode optical fiber is etched with hydrofluoric acid, and then the depression formed after etching is filled with ultraviolet glue to form a Fabry-Perot cavity. The Fabry-Perot cavity and the single-mode fiber Bragg grating are cascaded to form the sensing structure. The Fabry-Perot cavity is sensitive to temperature and refractive index, while the fiber Bragg grating is sensitive to temperature but not to refractive index. Using the above characteristics, the sensitivity matrix method can be used to achieve simultaneous measurement of temperature and refractive index. Experimental results show that the temperature and refractive index sensitivities of the sensor are -0.4832nm/℃ and -508.64pm/RIU, respectively. The sensor has the characteristics of a simple manufacturing process, compact structure, low cost, and high sensitivity, and has good application prospects.