Abstract: In order to measure refractive index of liquid with high-precision and low-cost,a liquid refractive index sensor based on a micro-hole in the single-mode fiber was fabricated by means of water-assisted femtosecond laser ablation method.The responses of transmission loss of the sensor to the refractive index and micro-hole length were investigated.Based on the ray theory,the sensing mechanism was analyzed.The effect of temperature disturbance on the sensor performance was also discussed.The experiment results show that the sensor has a good linear response in the refractive index range of 1.333~1.413,the sensitivity of the sensor can achieve 157.48dB/RIU and it is less susceptible to temperature change.Compared with other fiber refractive index sensors,optical fiber micro-hole sensors have the outstanding advantages,including compact,easy to fabricate,high sensitivity insensitive to temperature and low cost,etc.Therefore optical fiber micro-hole sensors can have extensive application in the fields of biochemical measurement.