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.