An in-line Mach-Zehnder interferometer (MZI) for simultaneous measurement of temperature and refractive index (RI) is proposed and demonstrated. The sensor is composed of cleaved taper, single-mode fiber (SMF) and spherical structure. Using precision device to measure the position of waist, the cleaved taper structure is obtained by cutting the taper structure. The sensitivities of the temperature are 0.052 nm/℃ and 0.037 nm/℃ in the temperature range of 25—70 ℃, respectively. The RI sensitivities are -56.59 nm/RIU and -43.53 nm/RIU in the RI range of 1.335—1.38, respectively. This sensor has many advantages such as compact structure and good stability.