In order to improve the detection sensitivity of brucella antibody and discover diseased livestock earlier for reducing economic losses, a disposable label-free immunosensor for rapid and quantitative detection was prepared. It was made by modification of cysteamine onto screen printed gold electrode surface and immobilization of antigens. By the method of cyclic voltammetry, it was shown that there is a linear relationship between the changes of peak current and the different brucella antibody concentrations within the range of 10-5~10-3IU/mL, the relevant correlation coefficient is 0.9999 and the lower detection limit is 2.8×10-5IU/mL. Furthermore, semi-differential transformation was applied to all of the cyclic voltammograms, the correlation between the changes of semi-differential values and the corresponding concentration of brucella antibody has been established, the correlation coefficient is 0.9929 and the lower detection limit is 2.7×10-6IU/mL in the range of 10-5~10-3IU/mL, and the correlation coefficient is 0.9992 in the range of 10-2~1IU/mL. It was shown that the detection range and the lower detection limit were improved greatly by the semi-differential transformation.