The invention discloses a vehicle-mounted fatigue early warning device and a method thereof. The vehicle-mounted fatigue early warning device comprises an image acquisition unit, an image processing and positioning unit, a fatigue detection unit, a control unit used for controlling the coordinated operation of all functional units and a warning unit. The method comprises the following: the first step, acquiring pupil image data; the second step, position-processing the acquired pupil image data; the third step, working out a pupil area, and judging whether a driver is tired according to the percentage of eye-closing time against unit time; and the fourth step, sending out a warning signal according to a judging result. The device uses an FPGA chip, and realizes the eye positioning algorithm in a mode of digital circuit system. Compared with the prior art, the device has the advantages of high real-time response, quick and timely early warning on fatigue, small volume, low power consumption, convenient assembly and the like, so that the device is quite suitably applied to a vehicle-mounted electric system.