The optical fiber sensor of traditional SMS structure has such problem as single mode and large loss

thus causing low temperature sensitivity and inaccurate sensing and displaying data of electrical equipment. In this paper

a new optical fiber Mach-Zehnder interference sensor with single-mode-multi-mode-multi-mode-single-mode structure is adopted to improve the original structure. The coupling of large core multi-mode optical fiber with singlemode optical fiber on both ends achieves beam splitting and beam merging and

at the same time

the large core multi-mode optical fiber with small multi-mode fiber（MMF

2

）are spliced so to kee

p the higher order mode and base mode enter into small core multi-mode fiber cladding and fiber core for transmission

thus generating phase difference and eventually forming mode interference mode which is sensitive to temperature. Moreover

the temperature sensitive characteristic of the structure is theoretically analyzed. The temperature sensitivity can be improved up to 80 pm/℃by using two structures of MMF

2

sensors with lengths of 8 mm and 12 mm respectively. At the same time

the structure has lower strain sensitivity

which can better avoid the impact due to stress changes. In addition

the structure has such advantages as low strain cross sensitivity

simple fabrication

low cost and low loss and has a broad application prospect in the field of temperature monitoring.