A temperature and refractive index sensor based on fiber Bragg grating (FBG) end surface cascade open Fabry-Pérot (FP) cavity has been designed and demonstrated experimentally. The open FP cavity has been fabricated on the end face of an FBG by dislocation fusion in this work, the open FP cavity could be used for refractive index sensing, and the temperature is measured by the FBG. The working principle of the sensor and the method of improving the sensitivity are analyzed by theoretical simulation. The refractive index sensitivity of the sensor is 1 108.4 nm/RIU, while the maximum fluctuation of the sensor stability experiment detection is 0.005 nm. The results show that it has satisfactory characteristics. The sensor is a compact all-fiber structure, so it has potential applications in the field of temperature refractive index sensing, such as biomedical and capacitor electrolyte detection.