The invention belongs to the technical field of electrolytic aluminium production. For solving the problem of inaccuracy for calculating heat aluminium working hours of a key part of an electrolytic aluminium continuous casting production line, the invention discloses a method for monitoring a service life of the key part of the electrolytic aluminium continuous casting production line. The method comprises the steps: (1) detecting signals such as a complete machine power supply signal, a casting ladle lifting signal, a casting machine operation signal, a printing head automatic signal and the like and executing the step (2) if the signals are all in an on state; (2) reading current operation frequency omega of a frequency converter and then according to the following formula, calculating time T of casting a single aluminium ingot and Te required by a heat aluminium casting die for operating to a casting machine head from the position of a casting ladle; (3) calculating the heat aluminium working hours Twhole of the key part. According to the method, accuracy of calculating the heat aluminium working hours Twhole of the key part is improved, so that an operator can timely replace the key part of which the service life is to be end and the electrolytic aluminium continuous casting production line is guaranteed to uninterruptedly operate for a long time.