Two different surface treatments were adopted to form the film layers whose equivalent circuits were simulated by electrochemical impedance measurement. Discharge performance of each treated surface was studied by the electrochemical, potential step and current step in sodium chloride solution. The microstructures of treated and blank magnesium were observed by scanning electron microscopy (SEM) before and after discharge. According to the SEM observation, the discharge process of the sample treated by the nickel electroless plating had been deduced. For the electroless magnesium alloy, the experiments have proved that not only does the activity appear in the range of coating thickness, but the activity continues in the substrate metal under coating.