A sensor based on Mach-Zehnder interference structure is designed to measure refractive index and temperature simultaneously.The sensor structure is single mode-multi-mode-thin core-multi-mode-single mode.BeamPROP module of RSoft optical simulation software was used to simulate and analyze the optical field inside the sensor structure.The optimal length of the multi-mode fiber (MMF) and the thin core fiber (TCF) was determined.The sensor structure was made and the experimental system was set up to observe the refractive index and temperature response.Dual-parameter measuring simultaneously was realized combined with sensitivity matrix.The experimental results show that the sensitivity of the sensor is -44.944 nm/RIU in the refractive index range of 1.333—1.380 and 0.082 9 nm/℃ in the temperature range of 30—65 ℃.The proposed sensor has the advantages of simple structure, small volume and high sensitivity,which can provide reference for the design of dual-parameter sensor of refractive index and temperature.