An optical fiber sensor based on Mach - Zehnder interferometer (MZI) is proposed and experimentally demonstrated for the measurement of temperature and refractive index simultaneously.It is composed o f a pair of spherical-shape structures and an embedded taper,where the spherical -shape structure excites high-order cladding modes,and the taper enhances the penetration depth range of evanescent field.When the light launching in the core encounters spherical-shape 1,part of light is excit ed into cladding forming cladding modes,while other light continues transmitting in the core forming fundamental mode.The fund amental mode and cladding modes have optical path difference because of different refract ive indices.And the cladding modes could recouple with the fundamental mode and interfere at the spherical-shape 2.Experimental results show that the interference peaks of the transm ission spectrum have different sensitivities to temperature and refractive index,so that a matrix can be used t o achieve the simultaneous measurement of the temperature and refractive index.Within the range of 10-100℃ and 1.3432－1.4026RIU,temperature resolution and refractive index resolution of ~0.22℃ and 1×10－4RIU can be ach ieved by intensity-modulation.We also find that the temperature resolution is 0.37℃ by wavelength-modulation.