A high sensitive refractive index sensor based on the cladding etched photonic crystal fiber (PCF) Mach-Zehnder interferometer (MZI) is proposed,which is spliced a section of photonic crystal fiber between two single modes fibers (SMFs).The interference fringe of the MZI shifts with the variation of the ambient refractive index (RI).It is found that the RI sensitivity slightly decrease with an increase in the interference length.The sensitivities of MZI with 35mm PCF,40mm PCF,and 45mm PCF are 106.19nm/RIU,93.33nm/RIU,and 73.64n/RIU,respectively,in the range of 1.333 to 1.381.After etched,the RI sensitivity of the MZI could be improved obviously.The RI sensitivities of the MZI with 35mm PCF are up to 211.53nm/RIU and 359.37nm/RIU when the cladding diameter decreases to 112 μm and 91 μm,respectively.Moreover,the sensor is insensitive to temperature,and the measured sensitivity is only 9.21pm/℃ with the range from 20 ℃ to 500 ℃.In addition,the sensor has advantage of simple fabrication,low cost,and high RI sensitivity.