All-fiber Fabry-Pérot based on ring reflector structure is fabricated by orderly splicing two section of hollow fibers with different core diameters to the light induced single-mode fiber. As the small hole in the ring surface is easy for gas or liquid in and out the cavity,it is useful in detecting the refractive index of gas and liquid. The forming theory of the fiber optic Fabry-Pérot cavity is analyzed,and the refractive index sensor base on ring reflector is studied by experiments. A resolution of the refractive index 1.652×10-6 is obtained in a measuring refractive index experiment. It can be anticipated that the Fabry-Pérot refractive index sensors with ring reflector will have important applications in the fields of the toxic,flammable,explosive gases and low viscosity liquid refractive index or content detection.