Critically ill related neurological complications are one of the common causes of high mortality and morbidity in critically ill patients. Brain function monitoring techniques so far includes transcranial Doppler, quantitative electroencephalography, and mixed venous oxygen saturation of jugular bulbs. Most of them require invasive operation, and some are not sensitive enough to detect the hypoxic state of the brain which difficult to effectively identify patients who under the risk of critically ill related brain insufficiency. Near-infrared spectroscopy counts rely on a non-invasive device that uses infrared light to penetrate human tissue and estimates tissue oxygenation by measuring tissue uptake of infrared light. We review the strengths and weaknesses of brain oxygen saturation monitoring techniques that based on the near-infrared spectroscopy in this paper, as well as the evidence to detect the cerebral oxygen supply and demand disorders and to assess whether this technique guided management can reverse the balance of cerebral oxygen supply and consumption to prevent long-term neurological sequelae such as delirium and reduce ICU length of stay and mortality.