Background　Functional near infrared spectroscopy （fNIRS） is a non-invasive brain mapping technique with high temporal resolution. Optical topography， based on fNIRS technique， can display the hemodynamic changes of cerebral cortex under different cognition load through multi-site measurement of oxygenated and deoxygenated hemoglobin variations.　Objective　It is discussed that the changes of oxygenation status in different cerebral cortex under various cognitive tasks.　Content　The basic principle of fNIRS and its application in neurocognitive studies are reviewed.　Trend　fNIRS is of great reference value for future studies in the mechanisms of general anesthesia and impacts of the impact of anesthetics on on neurological function and cognitive development.