In order to research the magnetic-optical characteristic, an all fiber-optical structure system is built to measure the fibers′ Verdet constant based on the Faraday effect. The system′s theoretical model is built with the Jones matrix. Through analysis and simulation, it is shown that the input fiber can influence the measurement result, while the result is independent of the output fiber contrarily. Meanwhile the optimum length of the measured fiber is confirmed. Experimental system is built to measure the SMF-28e fiber′s Verdet constant. The measurement results prove that the Verdet constant of the SMF-28e fiber is 0.52±0.01 rad/(T·m), and the measurement results range from 0.52 rad/(T·m) to 0.56 rad/(T·m). Experiment is also taken under different driving voltages, and the result shows that the system has good linearity and feasibility, which also demonstrates the reliability and slability of the system.