Whatever the reason - the power supply voltage fluctuation, the environment medium conductivity changes, or circuit parameter drift, make the output increase, rising electricity point potential, increase the sampling signal, sampling signal is added to the potentiostat is magnified inverting input, compared with the control in the positive phase input signal after the amplifier amplification ratio drops, polarization control output power is reduced, Make the electrification point potential drop, return to the original set control potential value; Similarly, if some reason causes the galvanizing point potential to drop, the sampling signal obtained by the reference electrode drops, and the amplification factor of the amplifier increases when compared with the control signal, the output of the control polarization power supply increases, the galvanizing point potential rises and returns to the original set control potential value. That is, when any external or internal reason caused by the protection of the potential to the ground change, the potentiostat can increase or decrease the output correspondingly to change the potential back, so that the current point potential remains unchanged.