A optical fiber sensor based on Mach-Zehnder interferometer (MZI) is p roposed and experimentally demonstrated for the simultaneous measurement of temperature and pressure.The sensor adopts the structure of multimode fiber-thin core fiber-multimode fiber (MTM). When the light in the core of multimode fiber (MMF) reaches the first melting point of MMF and thin core fiber (TCF),some goes into the core of TCF for exciting core mode,and the other goes into the cladding of TCF for exciting cladding mode.When the two parts of light reach the second melting point of MMF and TCF,the light in the core of TCF goes into the core of MMF,part of light in the cladding of TCF goes into the cladding of MMF,and the other part goes int o the core of MMF,interfering with the core mode.The interference spectrum will shift with the changes of ext ernal environment,such as temperature and pressure.So the measurement of temperature and pressure can be realized by observing the MMF shift of interference valleys in the spectrum.The experimental results show tha t temperature sensitivity of Dip1and Dip2are 0.0424nm/℃ and 0.0519nm/℃,respectively,with the range from 30℃ to 90℃. Pressure sensitivity of Dip1and Dip2are －0.2406nm/N and －0.5244nm/N,respectively,with the range from 0.98N－9.8N.Because the temperature sensitivity and pressure sensitivity of Di p1and Dip2are not the same, respectively,simultaneous measurement of temperature and pressure can be realiz ed by using sensitivity matrix. This sensor has the advantages of easy made and low cost,and has certain resear ch and application value.