Circadian rhythm sleep-wake disorder has been proven to be one of the risk factors for cognitive impairment in the elderly. Understanding life function from the perspective of rhythm reflects one of the characteristics of the holistic view of traditional Chinese medicine. The Yellow Emperor′s Inner Classic（《黄帝内经》） believes that circadian rhythm of ying-wei（营卫） for day and night is the internal basis for sleep activities. This paper explored the correlation between circadian sleep-wake rhythm and mild cognitive impairment in the elderly from the following aspects: the physiology and pathology of ying-wei and its correlation with circadian rhythms; cognitive impairment deteriorated by disruption of circadian rhythm; and the treatment according to the time.