Abstract: In order to realize the simultaneous measurement of magnetic field and temperature, a Mach-Zehnder interferometer based on sphere-thin core fiber-sphere sensing structure was fabricated. The double parameter sensing was studied by using magnetic fluid as the sensing structure external environment. When the external magnetic field and temperature change, the refractive index of magnetic fluid changes regularly, and the magnetic field and temperature can be measured at the same time. But the extinction ratio of the structure is poor, so a spherical-multi mode fiber-thin core fiber-sphere sensor structure is improved. The results show that the magnetic field and temperature sensitivity of the sphere-thin core fiber-sphere sensing structure obtained by single-peak demodulation are -0.0967 nm/mT and 0.0667 nm/℃, respectively. The improved sphere-multi mode fiber-thin core fiber-sphere structure has a good interference effect, and the magnetic field and temperature sensitivity are 0.1267 nm/mT and -0.1213 nm/℃, respectively. It has the characteristics of low cost, high sensitivity, noise resistance and good application. The research can provide reference for the design of magnetic field and temperature double parameter sensor.