An apparatus for determining whether the brain is fatigued may include: an electroencephalogram signal collection module for collecting electroencephalogram signals of a testee; a quantization processing module for quantifying the electroencephalogram signals utilizing a sample entropy algorithm to obtain a final sample entropy value of the electroencephalogram signals; and a fatigue state determination module for determining whether the brain of the testee is fatigued according to the final sample entropy value, wherein it is determined that the brain of the testee is in a fatigue state when the final sample entropy value is within a predetermined range.