A biconical MachZehnder interferometer based on photonic crystal fiber is designed, and its refractive index (RI) sensing characteristics are studied. The sensor performance was simulated by FDTD Solutions, and the results show that the transmission spectrum is redshifted with the increasing RI and the sensitivity is 95.906nm/RIU. An experimental platform was built to test the sensor under different concentrations of glycerin solution, and the response relationship between its transmission spectrum and external refractive index was studied. The experimental results show that with RI changing from 1.3222 to 1.3538, the sensitivity is 121.95nm/RIU@1550nm. The RI sensor with the characteristics of high RI sensitivity, easy fabrication and lowcost is suitable for applications in the biochemical and physical sensing fields.