Objective To investigate the semi-conducting property of passive films formed on brass under different passivation potential. Methods The passivation range of brass in borate buffer solution was obtained by potentiodynamic polarization curves, and three passivation potentials were chosen. The electrochemical impedance spectroscopy and Mott-Schottky theory were used,and the diffusion coefficient of passive film was calculated using PDM. Results The brass showed obvious passivation state in borate buffer solution. The Mott-Schottky plots were linear with a negative slop. With the passivation potential moving towards positive, the film impedance increased, the acceptor density and the flat potential decreased, the space charge layer thickness increased, and the order of magnitude of point defect diffusion coefficient was 10^-14. Conclusion Under different passivation potential, the passive films on the brass surface showed the property of p-type semiconductor, the majority of the carriers in the passive film were holes. With the passivation potential moving towards positive, the conductivity of the film decreased and the corrosion resistance was improved, resulting in better protection.