Abstract: The deterioration mechanism of a 300 kA large-scale prebaked aluminum reduction cell was studied. After a shutdown, the cell was dissected dryly for sampling analysis and observation, then the deterioration of carbonized cathode was investigated, such as breakage, leaks and surface corrosion pits. It was revealed that the causes of cathode's expansion cracking are mainly the sodium penetration, Al4C3 formed on cathode surface, electrocapillarity and electrolyte penetration into cathode gaps. Discusses the influencing factors on the service life of the cells were carried out. To lengthen the service life of the reduction cell, the following measures are regarded as efficient and suggested to take: improving the quality of carbonized cathode, strengthening the management of electrolysis cell from the very beginning and introducing such newly-developed materials and technologies as the graphitized cathode. In this way the voltage drop on cell bottom can be decreased so as to maintain well the cell wall.