The behavior of Fe in pipeline magnesium electrolysis was studied by means of electrochemical workstation, gas-cooled cathode and molten salt comprehensive analyzer. The results show that Fe is liable to cause current loss and magnesium loss. The current density, cell voltage, electrode material, reaction time, electrolyte temperature and electrolyte disturbance are the main factors affecting the purification of Fe. The purifying rate of Fe increases with the increase of cell voltage (lower than the decomposition voltage of MgCl₂), current density and reaction time, the purifying rate of Fe at graphite electrode is better than that at carbon steel electrode, and the purifying rate of Fe is the best when the electrolyte temperature is 725℃±5℃. In industrial production, by installing graphite DC electrode in the cell and controlling the voltage of graphite electrode within 6 V to 8 V, the purification rate of the cell can be improved. After industrial experiments, the impurity Fe in the electrolyte dropped from 0.028 9% to 0.009 1%, and the purification effect was obviously improved.