Cathode protecting method after aluminium electrolysis cell is shut

The invention belongs to the technical field of nonferrous metallurgy, and especially relates to a cathode protecting method after an aluminium electrolysis cell is shut. The method comprises the following steps: spraying a layer of coal tar on surfaces of a cathode carbon block group, a man-made ledge and a side carbon block; covering a layer of airproof film on the surface of the dry coal tar layer; and covering a pressing layer on the airproof film for preventing the airproof film from moving. Because an aluminium electrolysis cell cathode not subjected to protection restoration by employing the provided protection method is exposed in air for a long time when being used, the cathode is corroded by moisture and oxygen in air, and under the effect of high temperature and the relatively strong effect of external pressure, obvious cathode delaminating phenomenon and surface cracking phenomenon appear on the aluminium electrolysis cell cathode; and the delaminating probability of an aluminium electrolysis cell cathode is zero, and the surface cracking phenomenon is reduce by 70% in half a year, the restoration frequency of an aluminium electrolysis cell is obviously reduced, the cell-shut frequency is reduced to 2% from previous 10%, so that furnace restoration cost and cell shut cost are substantially reduced.