Since the existing optical fiber evanescent wave sensor sensitivity is not high, not easy to be encapsulated and other issues, the long segmented structure optic fiber sensor is proposed. The waveguide modes of the segmented structure and straight are simulated and analyzed by using Beam Propagation Method (BPM). The effect of the same core diameters, the different structures and the concentration of solution on the sensitivity of the sensors are investigated. The sensors of different structure parameters are fabricated with chemical corrosion method, and the sensitivity tested by using different concentrations of the methylene blue solution. The experimental results show that in the case of fixed corrosion depth, increasing the length of optical fiber sensing and segmented number can effectively improve the sensitivity and detection limit of the sensor, and the lowest concentration of the methylene blue solution can be detected up to the order of 10^{-6 mol/L. The sensor has the advantages of high sensitivity, simple structure, easy fabricated, low cost, which is suitable for materials spectrum measurements.}