For the improvement of traditional measurement method for solution concentration, a method of measuring concentration is proposed, which is based on the Fresnel principle in optical fiber. Through the Fresnel reflection formula and the relationship between refractive index and concentration, the concentration-dependent power changes are demonstrated, and the characteristics of the reflected power changes are also analyzed correspondingly. The reflected power should change with the variation of solution concentration and keep a good linearity. Furthermore, the experimental research prove the linearity between the power and solution concentration by using the sucrose solution and glucose solution, and the linear fitting factor is more than 99%. This method can be used for on-line measurement of the concentration of sucrose, glucose and other solutions, which has high linearity, simple operation, and easy to be operated.