In order to overcome some deficiencies of the traditional optic fiber chemical sensor, the intrinsic optic fiber chemical sensor based on evanescent wave theory was proposed. The relationship between sensitivity and geometrical structure parameters, the refractive index of solution were calculated and analyzed based on ray theory. The sensors of different structure parameters were fabricated with chemical corrosion method, the experimental system was designed and the test was carried out for these sensors using the methylene blue solution. The experimental results are concordant with numerical results, and the thinner, longer the sensing area is, the higher the sensitivity is.