General sensors have high sensitivity, but they are bulky and not easy to package. Fabry-Perot(F-P) cavity type sensor has been widely concerned for its simple structure, small size and easy packaging. An F-P cavity refractive index sensor is formed by fusing two different refractive index optical fibers and immersing the sensing fiber cladding in the liquid to be measured. The minimum resolution of the sensor is 3.0135×10-4, the length of sensing optical fiber is only 15 μm, the size is far smaller than other F-P cavity interferometers, and the accuracy of the length of sensing optical fiber is very low, so it is easy to manufacture.