To solve the problem of cross sensitivity between temperature and refractive index in liquid refractive index detection,an optical fiber sensor for temperature and refractive index dual parameter measurements of a sensitivity enhancing fiber Bragg grating(FBG)cascaded Mach Zehnder(M Z)structure is proposed in this paper.First of all,through multiple welding experiments,the single mode fiber(SMF)and thin core fiber(TCF)are tapered and welded adjusting welding parameters.Then,the other end of the TCF is fused with the head of the coreless fiber(NCF)to prepare a miniature M Z optical fiber interferometer.Finally,the fiber grating(FBG)encapsulated by aluminum capillary sensitization is cascaded at the end of the coreless fiber to complete the preparation of the optical fiber sensor for dual parameter measurement.According to the M Z interference principle and the FBG mode theory,the temperature sensitivity of the sensitized FBG theory is calculated,and the sensitivity coefficient matrix of the sensor and the theoretical formula of the wavelength offset of the temperature,refractive index and transmission spectrum are given.A temperature and refractive index sensing test system was built.The experimental results show that in the temperature range of 15～85℃,with the increase of temperature,the transmission spectrum of the sensor gradually shifts toward long wave.The linear correlation coefficients of the temperature and wavelength offset of the packaged FBG and M Z structures are 0.96323 and 0.91577 respectively,and the temperature sensitivity is 33.71 pm/℃ and 11.58 pm/℃ respectively.At room temperature(25℃),the refractive index of liquid is in the range of 1.333 RIU to 1.34235 RIU,as the refractive index increases,the FBG transmission spectrum doesn′t shift,but the M Z transmission spectrum gradually shifts toward shot wave.The linear correlation coefficients of refractive index and wavelength offset are 0 and 0.98761 respectively,and the refractive index sensitivity is 0 nm/RIU and -493.51322 nm/RIU respectively.The proposed sensor can effectively improve the detection accuracy and sensitivity of temperature and refractive index,and can be applied in the fields of environment,biology,petrochemical industry and food production.