A symmetric Mach-Zehnder interferometric sensor based on a seven-core fiber and a single-mode fiber ball is proposed. A single mode fiber end face is fused to fabricate a fiber ball with 180 μm diameter. A seven-core fiber is splicing between the two fiber balls. The length of the seven-core fiber in the middle of the Mach-Zehnder interferometer（ MZI） structure is 9 mm. The optical path difference（ OPD） between the fiber core fundamental and cladding modes of the sensor can be varied with the changes of outer circumstance temperature or curvature

which will caus

e the change of interference spectrum. The measurement of the external physical quantity can be achieved by monitoring the change of the interference spectrum. The simulation results of finite difference beam propagation method show that the fiber ball structure increases the optical coupling efficiency of seven-core fiber

and the interference effect of the seven-core fiber structure is improved effectively. The experimental results show that the temperature sensitivity of the sensor is 58. 97 pm/℃ with the linearity 0. 996 22

when the temperature changes in the range of 20～ 95 ℃

and the sensor has a curvature sensitivity of 2. 55 nm/m

-1

with a linearity 0. 996 73 at the range of 0～ 1 m

-1

. The proposed Mach-Zehnder interference sensor has compact structure

simple manufacturing process and high reliability.