Based on the fused tapered photonic crystal fiber (PCF), a Mach-Zehnder interferometer is proposed. The both ends of PCF is joined in a splice with a single-mode fiber and the interference fringe contrast of the transmission spectra is 2.23 dB. The transmission spectra of sodium chloride solutions with different mass concentrations are obtained. The corresponding relationships between the transmission spectra and external refractive index are analyzed. The experimental results show that the refractive index sensitivity of the sensor is 210.075 nm/RIU in the index range of 1.333~1.349, by measuring different mass concentrations of the sodium chloride solutions. In the temperature range of 20 ℃~70 ℃, the temperature sensitivity is about 0.0018 nm/℃ . This sensor is able to overcome the problem of cross sensitivity of temperature in the measurement.