This paper presents a driving fatigue monitoring method with machine vision algorithm, which is based on computing complexity. And a DSP system based on this method is also introduced. In this method, we firstly binarizated image which contains driver's facial information, to distinguish face area from background.. Then the binarizated luminance components is horizontally and vertically accumulated for collecting face pixel to draw out a face and eyes' location block. Thus, with accumulated index, analyze the relative location ratio between eyes and index of other facial parts, face width, and eyes horizontal position. Compare these ratios to PERCLOS based thresholds, we can ensure whether the driver's eyes are open or not , and infer drivers fatigue state. Finally, this method has been fulfilled with an intact device based on DSP system. Series of experiments indicate this contactless device has advantages of easy operation, sensitive response and splendid accuracy etc.