A novel miniature fiber-optic Fabry-Perot refractive-index sensor machined by 157 nm laser is proposed. The sensor head consists of a micro air F-P cavity near the tip of a single-mode fiber with a micro channel on the fiber tip. The micro channel is used as the entrance for medium under test. Two thin films are coated at reflective interfaces of the F-P cavity as mirrors to ensure high optical contrast, respectively. A RI resolution of 1 130.887 nm/ refractive-index unit is achieved by experiment. Compared with other fiber-optic RI sensors,the proposed sensor has a number of outstanding advantages including small,rigid,high resolution,excellent linearity,and wide measurement range,etc,which can meet the requirements for practical applications especially in biomedical diagnostic where small sensor size is essential.