The invention discloses a height adjusting device for a crust breaking air cylinder which is also named as a height adjusting device for a lower dead point of a crust breaking hammerhead and mainly used for height adjustment of the crust breaking air cylinder of an aluminum cell and the lower dead point of movement of the crust breaking hammerhead. The height adjusting device is characterized in that the height adjusting device is composed of a mounting fixing frame, spiral lead screws and a lifting connecting combination piece; and the lifting connecting combination piece can be driven by rotating the spiral lead screws, namely spiral sleeve pipes and air cylinder lifting connecting plates vertically move, namely a mounting fixing point of the crust breaking air cylinder can be driven to vertically move in a linear mode, so that the lower dead point of impacting movement of the crust breaking hammerhead is adjusted. The problems that fire eye feeding holes are difficult to form in the crusting positions of electrolyte due to the fact that the impacting depth of the breaking hammer of the aluminum cell is not in place, and due to the fact that the impacting depth of the breaking hammer is overlarge, and thus the hammer has a lump, fire eye feeding hole forming irregularity is caused can be thoroughly solved, and thus unattended operation and maintenance-free operation of the electrolytic cell are achieved.