A novel Fabry-Pérot (F-P) fiber-optic sensor for refractive index (RI) measurement is proposed. The sensor consists of a single-mode fiber end surface and a short air cavity which is close to this surface and produced by 157 nm laser micromachining. The light reflected from the end surface interferes with the light reflected from the air cavity. The fringe contrast of interference from the reflection spectrum of the sensor is influenced by the refractive index to be measured outside. The maximal contrast exists in the trough of the fringe envelop, and the refractive index outside can be gained through this contrast. The sensor can provide temperature-independent measurement of wide range of RI. In the range of 1.33～1.44,the RI sensitivity is about 27 dB, with resolution about 1.12×10-4; and in the range of 1.45～1.62, the RI sensitivity is about 24 dB, with resolution about 1.26×10-4.