The growth kinetics of the PbO layer has been further studied by linear sweep voltammetry. It is found that the PbO charge passed at a constant potential is proportional to the square root of the polarization time. During the growth of the PbO layer two different mass transfer processes appear in different potential ranges. Above 400 mV, its growth rate is controlled by the migration of the divalent O2+ vacancies passing through the PbO layer; while below 400 mV, it may depend on the migration of univalent ions, i.e., the OH- ion in the PbO layer and the H+ ion in the PbSO4 layer. The effects of the sweep rate are also discussed.