The separate detecting system of detecting Verdet constant of solute is designed based on Faraday effect principle. The detection technology can eliminate the impact of the background rotation such as solvents and containers to achieve the purpose of detecting Verdet constant of solute separately. The system used signal amplification processing technology based on a pair of optical paths to improve the system's detection sensitivity. Analyzed the detection accuracy and error of the system, the results shows that the detection accuracy is related to the accuracy with magnification of the division amplifier and Verdet constant of the reference material and sample material; and the relative error from the approximated calculation of small-angle is small. The technology of detecting the mixed solution concentration is researched under the relationship between the Verdet Constant and the concentration of the solute.