The invention discloses a fatigue monitoring and early warning system and a fatigue monitoring and early warning method based on a digital helmet, wherein the method comprises the following steps: acquiring electroencephalograph (EEG) signals of a user by virtue of an EEG collector which is integrated on the digital helmet, and analyzing a mental fatigue coefficient of the user according to the rhythmic change of the EEG signals; shooting an ocular image of the user by virtue of a camera which is integrated on the digital helmet, and analyzing a physiological fatigue coefficient of the user according to the ocular image; calculating the fatigue degree of the user according to the mental fatigue coefficient and the physiological fatigue coefficient of the user; and generating an alarm information including the fatigue degree of the user when the fatigue degree of the user exceeds a preset value of the user under normal circumstances, and transmitting the alarm information to a monitoring central platform by virtue of a communication network so as to early warning the fatigue status of the user. The system and the method disclosed by the invention, applied to digital battlefields, can be used for monitoring fatigue statuses of soldiers in real time during combat readiness or task execution of an army, and can be used for early warning soldiers in mental fatigue or physiological fatigue.