The relationship between current density and tank voltage has been studied when the oilfield sew age is treated by the electrocoagulation method.It is found that the current density throughiron electrodes is larger than that through graphite electrodes and much larger than that through aluminium electrodes when the tank voltage is the same.At the same current density, the tankv oltage decreases with the electroly te conductivity increasing.At the same tank voltage, the current density decreases with the space between electrodes increasing.The tank voltage of the monopolar electric tank is much less than that of the bipolar electric tank when the current density is the same.