With two ends of the multi-mode fiber and a single-mode fiber spliced together, a complex Mach-Zehnder interferometer is constructed by splicing fiber micropores with fibers of different core diameters. A new fiber optic sensor with high temperature and refractive index is constructed via the interferometer. Through experiment, it is found that the wavelength of the resonant peak valley in the transmission spectrum of the sensor linearly drifts only with the ambient temperature, while the peak intensity of the wave valley dip 1 linearly drifts only with the refractive index in the environment. A measurement matrix for temperature and refractive index of wave valley dip 1 can be obtained. The experimental results show that the high temperature sensitivity is 18.55 pm/℃ and the refractive index sensitivity is -155.2 dB/RIU (RIU is refractivity unit). Simultaneous measurement of the high temperature and refractive index is realized, and there is no cross sensitivity. The sensor has the advantages of compact and simple structure, stable performance and high sensitivity.