Based on evanescent wave absorbed theory, a segmented structure optic fiber sensor is proposed. The waveguide models of the segmented structure and straight are simulated and analyzed by using beam propagation method (BPM), which shows the high-order modes are excited repeatedly at the first transition of the each segmented region in the segmented structure. The effects of the different structures, core diameters and concentrations of solution on the sensitivity of the sensors are investigated, and the sensitivity is tested by using the different concentrations of the methylene blue solutions. The experimental results show that, with the fixed core diameters, the sensing region length of segmented structure sensors is 5 cm, which is shorter than that of the conventional single straight sensor 6 cm. However, the sensitivity of segmented structure sensors is 0.0135 L/mmol, which is higher than that of conventional single straight sensor 0.0102 L/mmol. The segmented structure evanescent wave sensor can effectively stimulate the fiber low-order modes to the high-order modes, and than the sensitivity is enhanced. The results are consistent with theoretical models and simulation analysis. The proposed sensor not only has a high sensitivity, but it is robust due to the larger core diameters and shorter length of the segmented region, which is suitable for materials spectrum measurements.